High back EMF, high pressure subwoofer having small volume cabinet, low frequency cutoff and pressure resistant surround

ABSTRACT

A subwoofer cabinet having a volume less that 1 ft 3  axially aligned openings in opposed cabinet walls; first and second cages mounted on respective ones of the walls in alignment with the openings; a voice coil driven driver including an annular 225 oz. magnet affixed to the first cage; a stationary pole piece extending through the magnet and defining a magnetic gap therebetween; a voice coil mounted on a cylindrical voice coil former positioned within the gap; a cone affixed to one end of the former; a first flexible surround secured to the outer end of the cone and attached at its periphery to the first cage; a flexible spider secured to the former and at its outer periphery to the first cage; a mass driven driver including a 1.7 lb. mass; a second flexible surround secured to the mass and to the second cage; a flexible spider attached to the second cage and to the mass; both surrounds having a uniform thickness of at least 0.1″, an edgeroll having a diameter of at least 1.5″, and capable of standing off internal pressures of 1.5 lbs./in 2  to 3 lbs./in 2 ; a drive amplifier capable of delivering 2,700 watts to a nominal 4 ohm resistive load and swinging 104 volts for delivering (+)-v and (−)-v drive signals to the voice coil for driving the voice coil driven driver through a peak-to-peak stroke of about 2.5″ while generating a large back emf sufficient to counter the applied emf and minimize current flow in the voice coil.

RELATED APPLICATIONS

The present Application is a Continuation Patent Application claimingpriority benefit of U.S. Ser. No. 08/909,892 filed on Aug. 27, 1997 andissued on Aug. 10, 1999 as U.S. Pat. No. 5,937,074, which is related to,based on, a continuation-in-part of, and, for all common subject mattercontained therein, claims priority from, Applicant's co-pendingProvisional Application No. 60/023,784, filed Aug. 12, 1996, entitled“HIGH BACK EMF, HIGH PRESSURE SUBWOOFER HAVING SMALL VOLUME CABINET, LOWFREQUENCY CUTOFF AND PRESSURE RESISTANT SURROUND”.

The present Application is also related to, a continuation-in-part of,and describes and claims improvements on, the invention disclosed andclaimed in Applicant's co-pending U.S. patent application, Ser. No.08/582,149, filed Jan. 2, 1996, entitled “HIGH POWER AUDIO SUBWOOFER”,now U.S. Pat. No. 5,748,753 issued May 5, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of high fidelityaudio reproduction; and, more particularly, concerns subwooferloudspeaker systems that produce high quality, low distortion andlow-frequency sound.

2. Prior Art

In the field of high fidelity sound reproduction, a high quality audiosystem is normally comprised of: a) a signal source, which is generallymusic or soundtracks from: i) films; ii) compact disk players; iii)laser disk players, and the like; b) a “preamplifier” which receivessignals from the signal source and provides an audio signal to a poweramplifier which amplifies the signal; and c), loudspeakers that canreproduce the sound from the signal source. Generally, loudspeakers aresingle enclosures designed to produce most of the audible frequencyrange, which is from 20 Hertz (“Hz”) to 20,000 Hz.

Modern recording technologies have allowed music and film Producers tomake recordings having wider dynamic ranges—i.e., higher signal-to-noiseratios—and more extended frequency response. Furthermore, many music andfilm recordings contain more low frequency information than those ofonly a few years ago. This is especially true in film soundtracks, whererecordings of special effects such as explosions are commonplace.

In response to the increased low frequency sound in recordings, agrowing number of audio systems are adding an additional type ofloudspeaker to their existing array of loudspeakers. This type ofloudspeaker is known as a “subwoofer”. Subwoofers are specializedloudspeakers which reproduce only the lowest frequencies of the audiblefrequency range—viz., those frequencies ranging from approximately 20Hz, or lower, to about 80 to 120 Hz. These low frequencies are difficultfor many full range loudspeakers to reproduce because the bass driversfor full range loudspeakers must handle a wider frequency range—i.e.,their frequency response must extend much higher in the audiblefrequency range, often to about 2,500 Hz or even higher depending uponthe design of the loudspeaker. Adding a subwoofer to an audio systemrelieves the full range loudspeaker from reproducing the lowestfrequencies, thereby improving its performance. In addition, certainstandards are being set for the reproduction of film soundtracks at homewhich require the use of one or more subwoofers. Such standards includeTHX® (a registered trademark of Lucas Film, Ltd.) certification fromLucas Film and Dolby AC-3 Surround Sound® (a registered trademark ofJ.C. Penney Company, Inc.) from Dolby Laboratories. Dolby AC-3 SurroundSound® even has an audio channel dedicated to only low frequencyinformation.

Conventional design of a subwoofer involves the placement of one or morelarge bass drivers into a large cabinet—e.g., typically a cabinetenclosing a volume of space ranging from about 8 cubic feet to about 27cubic feet. Bass drivers, known as “woofers”, generally include acircular “diaphragm” or “cone” which can be constructed of manydifferent materials including paper, plastic, kevlar, etc. Woofer coneshave a certain diameter—viz., the bore of the cone is equal topi×radius² (πr²). Prior art subwoofer cones capable of high acousticoutput generally have a diameter of at least ten inches, and oftengreater.

The circumference of the cone is affixed to a “surround” or“suspension”, which is then affixed to the driver's frame. Thesuspension enables the cone to move in and out of the driver frame at aparticular frequency and returns it to a null position when no sound isproduced. The peak-to-peak distance traveled by the cone is known as the“stroke” of the driver—sometimes referred to as the “excursion” of thedriver. Generally, the drivers installed in prior art subwoofers have apeak-to-peak stroke or excursion of between 0.4″ and 0.6″. Prior artsuspensions are constructed of flexible, compliant materials such asrelatively thin rubber, impregnated cloth, expanded synthetic cellularfoam such, for example, as expanded cellular polyethylene (“PE”)surround foam, or similar materials which are compressed to a thicknessof about 0.02″ and which are not self-supporting, which havehistorically produced very little resistance to peak-to-peak conemovement, and which are capable of standing off box pressures of only onthe order of nominally about 0.1 lbs/in² and, at best, only about 0.15lbs/in².

Movement of the cone about the suspension causes air to be moved, whichis what produces the sound heard and, in the case of bass, felt by thelistener. The amount of air that can be moved by a driver is directlyrelated to the bore and stroke of the subwoofer cone. Thus, to increasethe amount of air that a subwoofer can move, the bore, the stroke,and/or both the bore and stroke, can be increased. However, and as willbe discussed below, simply increasing the bore and/or the stroke hasdisadvantages.

At the center of the cone, the driver is affixed to the “motor” of thecone which is comprised generally of a single electrical conductorplaced within a magnetic field. In the prior art, the electricalconductor is a single electrical wire wrapped around a cylinder. Thisarrangement is know as the “voice coil” of the driver. The voice coil iswrapped around a voice coil former which is, in turn, affixed to thecone of the driver and placed in proximity to a magnet. When current isrun through the voice coil, magnetic fields are created around the voicecoil. These voice coil magnetic fields interact with the magnetic fieldsof the magnet, which causes the voice coil former to move. The voicecoil former's movement causes the movement of the cone. Cone movement,as discussed above, causes movement of air which produces sound.Producing sound at higher volumes requires greater cone movements.Greater cone movements are produced when the voice coil and the driver'smagnet have greater magnetic field interactions; and, this increasedmagnetic field interaction is produced when the voice coil has morecurrent running through it.

To reproduce low frequencies at high volume levels, a subwoofer must becapable of moving large quantities of air. Typical prior art subwoofersfor use in the home can move approximately one-hundred thirty cubicinches of air. For louder audio volumes, it is desirable that thesubwoofer be capable of moving even more air—for example, one-hundredeighty cubic inches of air. A typical fifteen inch diameter woofer,which has a cone diameter of approximately thirteen inches and a strokeof approximately 0.6 inches, can move approximately eighty cubic inchesof air. Therefore, generally a prior art subwoofer will utilize two ofthese drivers; and two drivers are able to move approximatelyone-hundred sixty cubic inches of air.

One disadvantage of having a driver with a fifteen inch cone is that itis difficult to design a cone of that size which is rigid enough toresist distortion when the cone has such a large surface area.

Another example of a prior art subwoofer utilizes four twelve inchdrivers. Each of these drivers has a cone diameter of approximately teninches and a stroke of approximately 0.6 inches. Such a subwoofer canmove approximately one-hundred ninety cubic inches of air. However, sucha subwoofer suffers from the disadvantage that four drivers arerequired; and, this greatly increases the size of the cabinet required,cost and weight.

Of course, it is possible to increase the stroke of the driver, and thusincrease the amount of air that is moved by the driver. However, whenthe stroke of the driver is increased, the efficiency of the driver issubstantially reduced, as less of the voice coil will remain in themagnetic gap.

Prior art subwoofer systems invariably require a large cabinet. Onereason, as seen from the above, is that many prior art subwoofer systemsutilize several large drivers so that they can move enough air foradequate performance. However, large cabinets are necessary for priorart subwoofers for reasons having nothing to do with the number ofdrivers installed therein. Some of the more significant reasons for thisare set forth hereinbelow.

Drivers for subwoofers are generally installed in a sealed or ventedbox. Thus, when the cone of the driver moves, it must overcome theforces inherently created because of the box structure itself. Forinstance, during operation, if the cone is moving into the cabinet, theair inside the cabinet will be compressed by the moving cone, therebycreating a force resisting inward cone movement. If, on the other hand,the cone is moving out of the cabinet, a vacuum is created that, ineffect, exerts a force tending to pull the cone back into the cabinet.These conditions exist for both sealed and vented boxes or cabinets.Atmospheric pressures outside the cabinet also affect these forces.

The driver must overcome the foregoing forces during movement of thecone. The higher the pressure to be overcome (whether positive ornegative), the more power that is required to overcome that pressure.The physical structure of the subwoofer can be manipulated to deal withthe increase in power that is required to overcome the foregoing forces.First, a larger enclosure (i.e., cabinet) can be used. A largerenclosure will create less resistance to inward and outward conemovements because it contains more air than a smaller enclosure. Thereason for this is that when the driver cone moves into the cabinet, thelarger air volume is compressed to a lower pressure. Thus, less power isrequired by the voice coil to overcome the forces created by thecompression of air within the cabinet. Further, when the driver conemoves out of the cabinet, less vacuum is created, which therefore allowsthe voice coil to move the cone with less power. Because of this, priorart subwoofers have typically utilized relatively large cabinets.

A second design factor is related to the stroke of the driver. If thestroke of the driver is short, the driver cone will have physicallimitations on how far it can enter into the cabinet and how far it canextend outwardly from the cabinet. The shorter the extension of thedriver cone into the cabinet, the less air that will be compressedwithin the cabinet. Such a movement will, therefore, require less powerinto the voice coil to effectuate movement of the cone. The same holdstrue for cone extension out of the cabinet. The shorter the extension ofthe driver cone out of the cabinet, the less will be the vacuum that iscreated and, therefore, the less power that will be required for suchcone movement.

Power in prior art subwoofer systems must be provided by poweramplifiers. Often a subwoofer system will use a separate poweramplifier. However, for ease of packaging, many prior art subwoofersystems utilize power amplifiers that are built into the cabinet of thesubwoofer. In general, power amplifiers capable of driving conventionalprior art subwoofers must be large and capable of creating betweenone-hundred (100) to three-hundred (300) watts of power. Large amountsof power are required to drive a subwoofer for many of the reasonsdescribed above. However, power amplifiers capable of providing suchpower levels tend to create large amounts of heat which, in turn,requires large heat sinks, massive power reserve capacitors, and largetransformers, all of which are large in size, heavy, and expensive. Allof these factors are undesirable; and, all tend to reinforce the needfor a relatively large cabinet.

Thus, as can be seen from the foregoing, because of the large powerdemands required by subwoofer systems and the large cost involved inproviding large amounts of power amplification, prior art subwooferapparatus have invariably required, and utilized, large cabinets whichheld drivers having large diameters and short strokes. Such anarrangement, as discussed above, allowed the subwoofer to movereasonable amounts of air without distortion. However, normal listeningenvironments often do not have space for such a large cabinet.Therefore, there is a need for a subwoofer system capable of producinglow frequency information at high listening volumes that is packaged ina small volume cabinet.

The design of audio woofers has, for many years, been predicated onconventional wisdom commonly referred to as “Hoffman's Iron Law” whichprovides:

Eff.=V _(BOX) /f ₀ ³ =kV _(BOX) /f ₀ ³  [1]

where f₀ is the desired low frequency cutoff or limit-for the subwoofer;V_(BOX) is the volume of the cabinet; and, Eff. is the efficiency of thesubwoofer. Unfortunately, if one wishes to reduce the low frequencycutoff (f₀) from, for example, 50 Hz to 18 Hz while retaining the sameefficiency, the volume of the woofer cabinet must be significantlyincreased. Or, if one wishes to decrease box volume from, for example, 1ft³ to 0.4 ft³ and, at the same time, decrease the low frequency cutoff(f₀) from, for example, 50 Hz to 18 Hz, efficiency drops by a factor ofapproximately 53. Consequently, the woofer designer finds that where a50 watt or 100 watt amplifier might have operated a 1 ft³ woofer at a 50Hz low frequency cutoff, a 0.4 ft³ box at 18 Hz low frequency cutoffwill require an amplifier that is approximately 53 times larger thanconventional.

For example, a typical loudspeaker in a 1 ft³ box with a low frequencycutoff of 50 Hz and one percent (1%) efficiency will normally operatesatisfactorily if it employs a 200 watt amplifier. But, were thedesigner to arbitrarily decide to reduce the box volume to 0.4 ft³ andthe low frequency cutoff to 18 Hz, the wattage requirement for theamplifier would be 10,600 watts. That, of course, would be ludicrous andis neither practical, cost effective nor economically feasible from acommercial standpoint.

In essence, Hoffman's Iron Law forbids one from making a subwooferhaving a small volume box, high efficiency and low frequency cutoff,and, designers of subwoofers have not deviated from religious adherenceto such theories. If the speaker designer wants to have a highlyefficient bass driver for a highly efficient woofer that can have a verylow frequency cutoff, the box must be huge—and, they always are.Conversely, if the designer wishes the box to be small, there hasheretofore been no way to get a lot of bass out of it, either low orloud, with high efficiency.

At the same time, speaker designers have been taught, and have believed,that there is an optimum size for magnets employed in voice coil drivenwoofers—i.e., it has been assumed that if the magnet is too small, thespeaker will not work at all; but, if the magnet is too large, only asmall percentage of the output wattage from the power amplifier will beapplied to the voice coil. Consequently, woofer designers have concludedthat an optimum magnet must lie somewhere between “too small” and “toolarge” in order to produce effective power in the voice coil. Typically,therefore, virtually all conventional subwoofers will employ a magnetthat weighs on the order of only about 20 ounces or less. Indeed, evenin the face of today's highly advanced technologies, speaker designersstill believe that a well designed, commercially marketable subwoofershould employ: i) a relatively large cabinet—e.g., from about eight toabout twenty-seven ft³; ii) multiple large drivers; iii) drivers withpeak-to-peak strokes generally on the order of not more than 0.4″ to0.6″; iv) magnets weighing, on average, not more than 20 ounces and, atthe very most, about 40 ounces; v) low internal box pressures of on theorder of only about 0.1 lbs/in²; and, vi), surrounds or suspensionsystems that are very compliant leading to surrounds that are, at best,flimsy and incapable of stably supporting the moving driver componentswithout wobble and consequent degradation of the audio sounds generated.

The problem of attempting to design a woofer which is small insize—e.g., defining an enclosed volume of space of about 0.4 ft³ toabout 0.5 ft³ having a low cutoff frequency below about 40 Hz, and whichis, at the same time, efficient, has defied solution—at least until theadvent of the present invention and the invention disclosed inApplicant's aforesaid co-pending U.S. patent application, Ser. No.08/582,149, filed Jan. 2, 1996, now U.S. Pat. No. 5,748,753 issued May5, 1998. For example, as stated by Louis D. Fielder of DolbyLaboratories, Inc. and Eric M. Benjamin in an article entitled“Subwoofer Performance for Accurate Reproduction of Music”, J. AudioEng. Soc., Vol. 36, No. 6, June 1988, pages 443 through 454 at page 446:

“For the required value of 0.0316 acoustic W at 20 Hz, this results in avolume excursion of 41.8 in³ (685 cm³). For a single 12-in (0.3-m)woofer effective piston diameter 10 in (0.25 m) this would require apeak linear excursion of 0.53 in (13.5 mm). This large excursionrequirement can be reduced by using larger drivers, increasing thenumber of drivers, and utilizing the low-frequency boost provided by theroom. With four 15-in (0.38-m) woofers the peak linear excursionrequired is 0.078 in (2 mm), neglecting room effects.”

In short, the “solution” advocated by the authors, who are accreditedexperts that were then attempting to establish design criteria for theperformance of subwoofers to be used for the reproduction of music inthe home, is: i) to design a woofer having a peak linear excursion of0.53″; ii) to attempt reduce this “large excursion”—i.e., 0.53″—by usinglarger drivers and increasing the number of drivers (and, therefore, thesize of the box or subwoofer cabinet); and iii), utilizing the lowfrequency boost provided by the listening room.

Those skilled in the art relating to subwoofers will recognize that theefficiency of a subwoofer is proportional the size of the box or cabinetthat the subwoofer is mounted in. Therefore, a box or cabinet that is{fraction (1/10)}th the size of a conventional prior art subwoofer boxor cabinet would ordinarily be ten times less efficient than its priorart counterpart. Under those circumstances, ten times more heat isdeveloped in the voice coil regardless of the efficiency of the drivingamplifier. Consequently, the voice coil will soon overheat; and, infact, that has been a major stumbling block to the development of verysmall, but powerful, subwoofers. Nevertheless, as will become apparentfrom the ensuing description, the present invention relates specificallyto a subwoofer characterized by its high efficiency and, at the sametime, its extremely small box or cabinet.

The broad concept of the present invention, in fact, flies in the faceof all known subwoofer computer modeling programs as well as theteachings in the prior art literature.

In this connection, those skilled in the art will appreciate that rawdriver efficiency is expressed as:

Eff.=(B1)² /r _(e)  [2]

where “B” is the magnetic field strength, and “1” and “r_(e)” areconstants.

Rewriting equation [2] it is found:

Eff.=kB ²  [3]

Based upon the foregoing, those skilled in the art will understand thatin a subwoofer driver where B is increased by a factor of 3.3, theefficiency will be increased by a factor of approximately 10—viz.,3.3²≅10. Unfortunately, however, when such a subwoofer driver is builtand installed in a box—any box—bass output is found to be actually farless than before the magnetic field was increased! This fact is wellknown to those skilled in the subwoofer art; and, consequently, priorart conventional subwoofers have evolved with magnetic fields optimizedfor maximum bass output.

Unfortunately, subwoofers designed with magnets optimized for maximumbass output are very inefficient. The reason for this is because themotor of the subwoofer (consisting of the voice coil and magneticstructure) is operating very close to stall, a condition characterizedby relatively high armature winding—or, in the case of subwoofers, voicecoil—heating. By increasing the magnetic field strength, the efficiencyis increased, but the bass output is decreased because of the large backemf generated by the motion of the subwoofer's voice coil immersed inits magnetic field. The magnitude of the back emf is established byLenze's Law:

back emf=dφ/dt,  [4]

where φ is the magnetic flux.

The back emf generated acts to prevent current from flowing in the voicecoil because it opposes the forward voltage impressed on the voice coilwinding. With the lowered current in the voice coil, the result is lessbass.

It must be recognized at this point that all prior art literature knownto the inventor, the descriptive equations therein, and all subwoofercomputer modeling programs based on prior art literature make the basicassumption that the subwoofer is operating in stall in order to simplifythe modeling. Prior to the advent of the present invention, thisassumption was tenable because a tracking downconvertor drive amplifierable to deliver the high voltage necessary to overcome the back emf didnot exist. Indeed, prior art subwoofer designers have all made thesimplifying assumption that the back emf at system impedance minimums isnot significant.

Another major problem encountered by subwoofer designers is directlyrelated to the fact that subwoofers are exceptionally prone to humproblems induced by power line “ground loops”. Ground loops are causedby a redundant ground that runs from the wall plug or other suitableA.C. source where the subwoofer is plugged in, through the power line towhere the audio signal source—e.g., a CD player, an FM tuner, aturntable, etc.—is plugged into the power line, and then back to thesubwoofer audio input through the audio cable shields. This constitutesa loop called a “ground loop”, and it generates a very undesirable 60 Hzhum.

Prior art subwoofers all suffer from unwanted “ground loop” induced 60Hz hum to a greater or lesser degree. Subwoofer designers have attemptedto solve the “ground loop” induced 60 Hz hum problem in various ways.One proposed solution includes the use of a balanced transformer whichbreaks the loop by virtue of its primary and secondary windings. Thetransformer can either be at the power line input (power transformer),or at the audio input (input transformer), or, for that matter, at bothlocations. Another attempted solution involves the use of opticalcouplings in which the audio signal is coupled by a light beam—i.e.,there is no ground connection. Both of the foregoing approaches havebeen effective in substantially reducing, but not eliminating, “groundloop” induced 60 Hz hum problems. This is because while they effectively“break” the ground(s), they do not suppress the hum voltage generatedacross the broken ground or grounds.

SUMMARY OF THE INVENTION

The present invention overcomes the foregoing problems and disadvantagesinherent in the design, construction and operation of conventional priorart subwoofers by providing a subwoofer design that is characterized by:i) a relatively small volume sealed cabinet—e.g., a cabinet defining anenclosed volume of space on the order of from about only 0.4 ft³ toabout only 0.5 ft³; or, substantially less than 1 cubic foot in volumein the exemplary apparatus illustrated (stated differently, the presentinvention requires a subwoofer cabinet which ranges from only about{fraction (1/15)}th to about {fraction (1/67)}th the size of thecabinets employed in conventional prior art subwoofers)—ii) a singlevoice coil driven woofer; iii) a mass driven woofer, sometimes referredto in the art as a “passive radiator”; iv) a relatively small, compact,power amplifier capable of delivering 2,700 watts rms to a 3.3 ohm (theresistance of the voice coil) resistive load (hereinafter, a “nominal 4ohm resistive load”) and swinging 104 volts rms; and v), an arrangementwherein the maximum peak-to-peak excursion of each of the voice coildriven woofer and the mass driven woofer is on the order of about 2.5inches as contrasted with prior art drivers having peak-to-peak strokesranging from only about 0.4″ to about 0.6″—i.e., an arrangement whereinthe maximum stroke of the drivers of the present invention is from aboutfive to about six times greater than achievable with conventional priorart subwoofer driver configurations.

As a result of the foregoing, a subwoofer embodying features of thepresent invention is characterized by its extremely small size, highefficiency, high power and high acoustically accurate sound levels, allwithout requiring large, heavy and costly heat sinks and/or storagecapacitors.

It is a general aim of the present invention to provide a small,compact, fully contained subwoofer capable of generating high quality,low distortion, and low frequency audio signals at high listeningvolumes, yet which is packaged in an aesthetically pleasing small volumecabinet.

More specifically, it is an object of the invention to provide asubwoofer capable of generating acoustically accurate low frequencyaudio signals at high listening volumes packaged in a relatively smallvolume cabinet.

A related object of the invention is the provision of a subwoofer havinga relatively small volume cabinet, yet which has power and soundcharacteristics at least equal to, if not substantially better than,conventional prior art subwoofers despite the fact that the subwoofer isonly a fraction of the size, weight and cost of similarly performing,commercially available, subwoofers. In achieving this objective, thesubwoofer of the present invention, including its electronic packages orcircuit boards, is generally fully contained in a cabinet occupying atotal volume of space significantly less than 1 cubic foot—e.g., fromonly about 0.4 ft³ to only about 0.5 ft³—rendering the subwooferunobtrusive to the user and facilitating easy placement of one or moresubwoofers in a listening room or in other living areas within a user'sresidence, office or like facility.

In one of its more detailed aspects, it is an object of the invention toprovide a relatively low cost subwoofer apparatus capable of equaling orexceeding the performance characteristics of conventional large and moreexpensive subwoofers; and, which is compact, light weight, aestheticallyattractive in appearance, and devoid of large heat sinks, massive powerreserve capacitors, large transformers, and the like.

A further objective of the present invention is to provide a subwooferapparatus which, despite its small size employing a cabinet having asealed volume of space substantially less than 1 cubic foot, is highlyefficient and capable of moving or displacing large volumes of air—e.g.,a volume of just under 200 cubic inches of air—in response to drivermovement through a peak-to-peak stroke of up to about 2.5″.

In another of its important aspects, it is an object of the invention totake advantage of the high back emf generated by using a relativelylarge magnet—e.g., a magnet weighing on the order of 225 ounces(approximately 14 pounds, 1 ounce) or, approximately an order ofmagnitude greater than the magnets commonly used in conventionalsubwoofers—to oppose current flow in the voice coil of a voice coildriven woofer so as to enable employment of a small compact trackingdownconvertor drive amplifier capable of outputting on the order ofabout 2,700 watts rms to a nominal 4 ohm resistive load and capable ofswinging 104 volts rms; and, which will, therefore, deliver only about150 to 200 watts (300 to 400 watts on a time limited basis) maximumpower to the voice coil, preventing overheating thereof and enablinggeneration of large quantities of power with high efficiency. The use ofsuch a large magnet roughly ten times the size of conventional prior artsubwoofer magnets serves to increase the field strength of the subwooferby a factor of 3.3 since field strength increases roughly as the squareroot of the magnet size.

Stated differently, in one of its important aspects it is an object ofthe invention to provide a subwoofer design employing a very smallcabinet and a unique tracking downconvertor drive amplifier which iscapable of generating sufficient power applied to the subwoofer's voicecoil to overcome the excess high back emf generated by the use of alarge magnet in combination with maximum voice coil peak-to-peak strokesof about 2.5″. As a result of attaining this objective, sufficientcurrent flows in the voice coil to produce the desired bass output; and,the subwoofer's efficiency is increased by a factor of approximately 10,effectively offsetting the loss of a box volume related efficiency.

A further objective of the invention is to provide a subwoofer capableof operating far from the stall mode—viz., an operating modecharacterized by very little output power and large amounts of currentflowing in the voice coil generating large amounts of heat that must bedissipated—wherein the subwoofer is characterized by high conversionefficiency and low joule (voice coil) heating.

Yet another important objective of the invention is the provision of asubwoofer capable of achieving an 18 Hz low frequency cutoff in a smallbox 11″×11″×11″ having an enclosed volume of space of from about only0.4 ft³ to only about 0.5 ft³ with high efficiency and at low cost. Inachieving this objective, advantage is taken of the usage of a massdriven woofer (sometimes referred to as a “passive radiator”) incombination with a voice coil driven woofer made in accordance with thepresent invention, thus reducing size, weight and cost of the overallsubwoofer.

In another of its important aspects, it is an object of the invention toprovide methods for forming a surround for a subwoofer which is capableof standing off pressures ranging upwardly to about 3 pounds per squareinch (3 lbs/in²)—for example,—from on the order of about one and a halfpounds per square inch (1.5 lbs/in²) to about 3 pounds per square inch(3 lbs/in²)—and the resulting surround—all as contrasted withconventional surrounds which are typically capable of standing offpressures of only about 0.1 lbs/in² to 0.2 lbs/in²; or, an improvementof up to thirty times the capability of conventional surrounds.

A further and more detailed objective of the invention is the provisionof improved buffer circuitry for processing audio signals which sumsboth the L+R and L−R audio signal components, retaining the L−Rcomponents (which are typically destroyed in a conventional subwoofer'saudio signal processing system) as part of the composite output signal,thereby enhancing the life, luster, depth and impact of the audio soundfor the listener.

Another detailed object of the invention is the provision of improvedprotection circuitry for essentially eliminating distortion resultingfrom clipping, overheating, overdrive, or impulsive wave forms.

Yet another important objective of the present invention is theprovision of circuitry which completely eliminates both undesirable“ground loops” and the voltage generated across broken grounds, therebycompletely eliminating the problem of “ground loop” induced 60 Hz hum.

It is a further object of the invention to provide a system formaintaining tinsel leads under tension during peak-to-peak reciprocationof the subwoofers' voice coil driven components so as to preventundesired noise resulting from slapping of the tinsel leads against thespeaker cone in the voice coil driven woofer.

DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome more readily apparent upon reading the following DetailedDescription and upon reference to the attached drawings, in which:

FIG. 1 is an isometric view depicting an exemplary subwoofer embodyingfeatures of the present invention;

FIG. 2 is a vertical sectional view, partly in elevation, takensubstantially along the offset line 2—2 in FIG. 1, here depicting therelationship of the voice coil driven woofer, shown in elevation, andthe mass driven woofer, shown in section, as they are mounted within anexemplary 11″×11×11″ cabinet cube;

FIG. 3 is an enlarged sectional view through the voice coil drivenwoofer illustrating details of the construction thereof;

FIG. 4 is an isometric view of an illustrative voice coil former and avoice coil wound thereabout which is suitable for use with the exemplaryvoice coil driven woofer depicted in FIG. 3;

FIG. 5 is a vertical sectional view through the mass driven woofer andthe voice coil driven woofer, respectively viewed in the left and rightportions of the drawing, here illustrating: i) portions of the fixedstationary frame of the apparatus with the casing, magnet, circuitboards and other fixed structural members removed for purposes ofclarity; and ii), the movable components of the woofers—viz., thesurround, spider and mass of the mass driven woofer; and, the voice coilformer, voice coil, speaker cone, spider and surround of the voice coildriven woofer—shown in solid lines in their neutral or null positions,in dotted lines at the limit of their outward or PUSH strokes, and indashed lines at the limit of their inward or PULL strokes;

FIG. 6 is an isometric view of an exemplary surround embodying featuresof the present invention and which is here employed with the mass drivenwoofer depicted in FIG. 2;

FIG. 7 is a vertical sectional view taken substantially along the line7—7 in FIG. 6;

FIG. 8 is a vertical sectional view similar to FIG. 7, but hereillustrating a surround suitable for use with the voice coil drivenwoofer and having its central disk-shaped portion removed;

FIG. 9 is a highly diagrammatic vertical sectional view depicting oneexemplary manufacturing process for making a surround in accordance withthe present invention, here showing fragmentary portions of cooperablecomplementary male and female dies and a fragmentary portion of multiplelayers of an expanded synthetic cellular foam such, for example, as anexpanded cellular polyethylene (“PE”) surround foam employed in themanufacture of a surround embodying features of the present invention;

FIG. 10 is a highly diagrammatic, fragmentary, vertical sectional viewsimilar to FIG. 9, but here illustrating the use of a single relativelythick sheet of an expanded synthetic cellular foam employed tomanufacture a surround embodying features of the present invention;

FIG. 11 is a highly diagrammatic, fragmentary, vertical sectional viewsimilar to FIGS. 9 and 10, here illustrating the male die fully insertedinto the female die so as to compress the expanded synthetic cellularfoam to form a finished surround of the type employed in the exemplarymass driven woofer and which embodies features of the present invention;

FIGS. 12A and 12B, when placed in side-by-side relation and viewedconjointly, comprise a block-and-line drawing here depicting, in highlydiagrammatic form: i) certain of the electrical architecture employed inaccordance with the present invention to process an audio input signal;and ii), an exemplary Master Protection Circuit for controlling theaudio signal being processed;

FIG. 13 is a highly simplified block-and-line diagrammatic drawing, hereillustrating additional electrical architecture employed with thepresent invention to accept the audio output signal from the circuitryof FIG. 12B, steer the positive and negative, portions of the audiosignal through respective ones of the (+) and (−) Tracking DownconverterPower Supplies, and deliver plus −v. and minus −v. audio signals to theDriver Amplifier of the voice coil driven woofer and thence to the voicecoil for enabling PUSH/PULL drive of the voice coil driven woofer;

FIGS. 14A and 14B, when placed in top-to-bottom relation and viewedconjointly, comprise a block-and-line diagrammatic drawing, heredepicting: i) an exemplary, but conventional, Input Power Supplycircuit; and ii), exemplary (+) and (−) Tracking Downconverter PowerSupplies and a Driver Amplifier which collectively define a trackingdownconvertor drive amplifier capable of delivering 2,700 watts rms to anominal 4 ohm resistive load and swinging 104 volts rms, which embodyfeatures of the present invention, and which are of the type employed inthe subwoofer depicted in FIGS. 1-3;

FIG. 15 is a graphic representation of a portion of a typical audiosignal wherein the apparatus of the present invention is intended toamplify the low frequency components of the audio signal;

FIG. 16 is a graphic representation here depicting the audio signal asoutput from the (+) Diode Steering Network wherein negative portions ofthe audio signal have been eliminated;

FIG. 17 is a graphic representation here depicting the audio signalshown in FIG. 16 in broken lines and the voltage signal input to theComparator from the Diode Steering Network which is here approximatelyrepresented in solid line form;

FIG. 18 is a graphic representation here illustrating the two signalsinput to the Comparator forming part of, for example, the (+) TrackingDownconverter Power Supply, with the voltage signal input from the DiodeSteering Network being depicted in solid line form and the voltagesignal input from the Power Output Feedback associated with the (+)Tracking Downconvertor Power Supply being depicted in broken lines;

FIG. 19 is a graphic representation of the control signal output fromthe Comparator and input to the Ramp Time Modulator in the (+) TrackingDownconvertor Power Supply shown in FIG. 14A;

FIG. 20 is a graphic representation of the voltage pulses generated bythe Pulse Generator forming part of the (+) and (−) TrackingDownconvertor Power Supplies;

FIG. 21 is a graphic representation of the wave transmitted to the RampTime Modulator in the (+) Tracking Downconvertor Power Supply and themanner in which the voltage control signal from the Comparator isimposed thereon;

FIG. 22 is a graphic representation of the pulses output from the RampTime Modulator in the (+) Tracking Downconvertor Power Supply resultingfrom the imposed Comparator control signal as reflected in FIG. 21;

FIG. 23 is a graphic representation of an illustrative series of currentpulses transmitted from the (+) Tracking Downconvertor Power Supply tothe Driver Amplifier associated with the voice coil in the voice coildriven driver;

FIG. 24 is a highly simplified schematic circuit drawing depictingexemplary Input Buffers embodying features of the present invention andwhich are here employed for summing and processing the L+R and L−Rcomponents of the input audio signal and outputting a composite audiosignal (L+R)+α(L−R)—or a(L+R)+(L−R)—which retains both the L+R and L−Rcomponents of the input audio signal;

FIG. 25 is a simplified schematic circuit drawing depicting an exemplaryExcursion Limiter employed with the present invention;

FIG. 26 is a schematic circuit drawing depicting an exemplary LowFrequency Auto-Throttle circuit employed with the present invention;

FIG. 27 is a schematic circuit drawing depicting exemplary embodimentsof a Clipping Level circuit, a Manual Throttle Set circuit, a ThermalIntegrator circuit, a Thermal Integrator Trip circuit, and a simplifiedImpulse Damper employed in the Master Protection Circuit of the presentinvention;

FIG. 28 is a schematic circuit drawing depicting an exemplary, generallyconventional, Woofer Servo circuit for reducing distortion of the audiosignal at the output of the woofer by comparing the movement of themovable driver components (which movement is typically non-linear ordistorted) with the undistorted input audio signal so as to produce adistorted audio output drive signal wherein the distortion is generallyequal and opposite to the sensed distortion of the movable woofer drivercomponents and thus eliminating, to the extent possible, detectableaudio distortions;

FIG. 29 is a schematic circuit drawing depicting an exemplary DiodeSteering Network for outputting positive and negative audio signals torespective ones of the (+) and (−) Tracking Downconvertor PowerSupplies, as well as outputting the composite audio signal to the DriverAmplifier of the present invention;

FIG. 30 is a schematic circuit drawing, partially in block-and-lineform, here illustrating the processing of audio signal informationthrough the Diode Steering Network, the (+) and (−) TrackingDownconvertor Power Supplies, and the Driver Amplifier employed with thevoice coil driven woofer of the present invention and, illustratingalso, typical, but exemplary, wave forms input to, and output from, theDiode Steering Network;

FIGS. 31A, 31B and 31C, when FIGS. 31A and 31B are placed inside-by-side relation and FIGS. 31B and 31C are placed in top-to-bottomrelation, and when FIGS. 31A-31C are viewed conjointly, comprise aschematic circuit diagram depicting the various circuit components ofthe (+) and (−) Tracking Downconvertor Power Supplies employed with thepresent invention, it being understood that those blocks pertaining tothe Ramp Time Modulator, Switch, Power Output Section, Power OutputFeedback and Comparator for the (−) Tracking Downconvertor Power Supplyare, except where otherwise indicated, identical to the correspondingcomponents in the (+) Tracking Downconvertor Power Supply and,therefore, the schematic details of such components in the (−) TrackingDownconvertor Power Supply have not been shown in detail;

FIG. 32 is a schematic circuit diagram depicting an exemplary DriverAmplifier employed with the voice coil driven woofer of the presentinvention;

FIG. 33 is a schematic circuit diagram depicting an exemplary GroundLoop Hum Eliminator which completely eliminates both undesirable “groundloops” and the voltage generated across the broken grounds, therebycompletely eliminating the problem of “ground loop” induced 60 Hz hum;and,

FIGS. 34A, 34B and 34C are fragmentary diagrammatic views respectivelydepicting the neutral or null position of the movable voice coil drivenspeaker cone, the maximum PUSH excursion of the speaker cone, and themaximum PULL excursion of the speaker cone, here particularlyillustrating operation of an exemplary spring-type expanded cellularsynthetic foam employed to maintain the tinsel leads under tensionduring PUSH/PULL excursions of the movable components of the voice coildriven woofer.

While the present invention is susceptible of various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and will herein be described in detail. Itshould be understood, however, that it is not intended to limit theinvention to the particular forms of the invention disclosed; but, onthe contrary, the intention is to cover all modifications, structuralequivalents, equivalent structures, and/or alternatives falling withinthe spirit and scope of the invention as expressed in the appendedclaims. Thus, in the appended claims, means-plus-function clauses andsimilar clauses are intended to cover: i) the structures describedherein as performing a specific recited function; ii) structuralequivalents thereof; and iii), equivalent structures thereto. Forexample, although a nail and a screw may not be deemed to be structuralequivalents since a nail employs a cylindrical surface to secure woodenparts together while a screw employs a helical surface, in the artbroadly pertaining to the fastening of wooden parts, a nail and a screwshould be deemed to be equivalent structures since each perform therecited fastening function.

DETAILED DESCRIPTION

Turning now to the drawings, exemplary embodiments of the presentinvention will now be described. Thus, referring first to FIG. 1, anexemplary subwoofer, generally indicated at 50, embodying features ofthe present invention has been depicted. As here shown, the subwoofer 50includes a cabinet 51 which encloses two drivers, generally indicated at52 and 54 (only driver 52 is visible in FIG. 1; and, the details of thetwo exemplary drivers 52, 54 are more specifically shown in FIGS. 2, 3and 5), which are each oriented in a PUSH/PULL configuration on oppositesides of the cabinet 51. That is, the visible driver 52 depicted in FIG.1 comprises a mass driven driver shown in greater detail in FIG. 2 andis mounted in one wall of the cabinet (here the left sidewall 55 of thecabinet 51 as viewed in FIG. 1) and fires in PUSH/PULL directions; whilethe second driver 54 (not visible in FIG. 1, but shown in elevation inFIG. 2 and in section in FIG. 3) is mounted in the opposite or rightsidewall 56 of the cabinet 51 in the illustrative embodiments of theinvention and simultaneously fires in corresponding PUSH/PULLdirections. That is, both drivers 52, 54 move simultaneously in a PUSH(or outward) direction and simultaneously in a PULL (or inward)direction.

In carrying out the invention, the cabinet 51 is a substantially cubicstructure with: i) a front wall (not visible in FIG. 1); ii) a rear wall58 comprising a control panel; iii) left and right sidewalls 55, 56(sidewall 56 is not visible in FIG. 1 but is visible in FIG. 2),respectively, within which the woofer drivers 52, 54 are mounted; iv) atop wall 59; and v), a bottom wall (not visible in FIG. 1), allpreferably constructed of a rigid, non-resonant, inert material such asMDF type particle board, wood, or the like. Each panel or wall can havea suitable finish applied thereto such that the subwoofer can match thefurnishings of the room where it will be installed. The drivers 52, 54may, if desired, be covered by an acoustically transparent material (notshown).

It will be noted upon inspection of FIG. 1 that the rear wall 58containing the control panel—i.e., the wall in the right foreground asviewed in the drawing—includes: i) a Power ON/OFF indicator light 60;ii) three control knobs for permitting manual adjustment of Bass Level(knob 61), Crossover Frequency (knob 62), and Phase (knob 64); iii) amanually operable toggle switch 65 for selecting between Video Contourand Flat operation; iv) one pair of right and left female input jacks 66and one pair of right and left female input posts 68 for permittinginputting of audio signals; v) one pair of right and left female outputjacks 69; vi) a fuse 70; and vii), an A.C. outlet plug 71 and power cord72. The audio signal input jacks 66, 68, 69 can be connected to anysuitable cables (not shown) which bring the audio signal to thesubwoofer 50.

The front, rear, side, top and bottom panels (i.e., sidewalls 55, 56,rear wall 58, top wall 59, and the front and bottom walls which are notvisible in FIG. 1) of the cabinet 51 are fixed to each other to form thecabinet using known techniques. The cabinet 51 is preferably sealed sothat air can neither enter nor exit. Feet 74 (FIG. 1) may be placed onthe bottom panel 75 (not visible in FIG. 1 but shown in FIG. 2) of thecabinet 51 which raise the subwoofer 50 off of the floor (not shown).The feet 74 are, in the illustrative apparatus, generally disk-shaped,of sufficient strength to support the subwoofer 50, and preferablyformed of non-skid material capable of providing some sound or vibrationinsulation.

In accordance with one of the important aspects of the presentinvention, and as hereinafter described in connection with FIGS. 2 and3, the exemplary subwoofer 50 employs two drivers—viz., a mass drivendriver or woofer 52 mounted in the left sidewall 55 of the cabinet 51 asviewed in FIGS. 1 and 2, and a voice coil driven driver or woofer 54mounted in the right sidewall 56 of the cabinet 51 as viewed in FIG. 2.While the voice coil driven woofer 54 has been shown only in elevationin FIG. 2, a sectional view disclosing details of the driver has beendepicted in FIG. 3.

It will be noted upon inspection of FIG. 2, that the mass driven woofer52 includes a stationary frame or cage 76 mounted in the left sidewall55 of the cabinet 51 for resiliently supporting the moving drivercomponents in a stable manner wherein the movable driver components areconstrained for PUSH/PULL movement axially out of and axially into thecabinet. The movable driver components in the mass driven driver 52comprise: a resilient, but semi-rigid, high pressure resistant surround78 formed of an expanded synthetic cellular foam such, for example, asan expanded cellular polyethylene (“PE”) surround foam and comprising agenerally circular element having an outer peripheral circumferentialflange 79, an annular half roll or “edgeroll” 80 integral with theflange 79 and terminating in an inner annular inturned or downturnedintegral flange 81 which is, in turn, integral with a flat central diskportion 82. A rigid backing plate 84 formed of paperboard, plastic orthe like is adhesively bonded to the central disk portion 82 of thesurround 78. A round rod-shaped metal mass 85 weighing approximately oneand seven tenths pounds (1.7 lbs.) is secured to the backing plate 84within a cardboard or paperboard cylindrical tube 86 by means of asuitable epoxy glue 88.

Finally, the movable components of the mass driven woofer 52—whichcollectively approximate two pounds (2.0 lbs.) in the aggregate—includean annular flexible spider 89 having a corrugated cross-sectionalconfiguration wherein the corrugations get progressively deeper towardsthe outer periphery of the spider 89. The outer periphery of the spider89 is fixedly secured to the frame or cage 76 of the mass driven woofer52, while its inner periphery is fixedly secured to the cylindricalcardboard or paperboard tube 86 surrounding the mass 85.

Considering next FIGS. 2 and 3 conjointly, it will be noted that thevoice coil 15 driven woofer 54 includes a stationary basket-like frameor cage 90 which is fixedly Amounted in the right sidewall 56 of thecabinet 51 as viewed in FIG. 2. The base of the frame 90 comprises anannular washer-shaped flange 91 which is secured to an annular metal topspacer 92 adjacent which is positioned an annular magnet 94 having anexternal diameter of approximately 7 and {fraction (11/16)} inches, aninternal diameter of approximately 3½ inches, a depth of approximately1.75 inches or slightly greater, and a weight of approximately 225ounces (approximately 14 pounds, 1 ounce). In the exemplary form of theinvention shown, the magnet 94 comprises a single-piece magnet having adepth or length of approximately 1.75 inches; but, as those skilled inthe art will appreciate, the magnet 94 can be formed of two or moremagnet segments which, when assembled in end-to-end relation, have theapproximate dimensional and weight characteristics hereinabovedescribed. The bottom face of the annular magnet 94 is spaced from anannular metal bottom plate 95 by an annular spacer 96. The finalstationary member of the voice coil driven woofer 54 comprises anannular pole piece 98 having an external diameter of approximately 3inches. The arrangement is such that the outer diameter of the annularpole piece 98 defines an annular gap 99—termed the “magneticgap”—between the pole piece 98 and the upper annular spacer 92 with theannular magnetic gap being approximately 0.1″ to about 0.25″ in radialwidth.

The movable components of the voice coil driven woofer 54 comprise: i)an expanded synthetic cellular foam surround 78′ such, for example, asan expanded cellular polyethylene (“PE”) foam surround, which issubstantially identical to the surround 78 employed with the mass drivenwoofer 52 previously described except that the central disk-shapedportion 82 of the surround 78 associated with the mass driven woofer 52has been removed in the surround 78′ employed with the voice coil drivenwoofer 54; ii) a speaker cone 100 having a funnel shape with its outerlarge diameter end 101 being adhesively bonded or otherwise fixedlysecured to the inner inturned flange 81 on the surround 78′; iii) acylindrical voice coil former 102 having an inner diameter slightlygreater than the outer diameter of the annular pole piece 98; iv) avoice coil 104 wound about the voice coil former and having an outerdiameter slightly less than the inner diameter of the upper annularspacer 92; v) a rigid dust cover or surround support 105 having a shapecomprising a segment of a sphere which is positioned within, and securedto, the funnel-shaped speaker cone 100 with the domed portion of thedust cover/support facing outwardly; vi) a decorative cover 106 formedof expanded cellular polyethylene (“PE”) surround foam, or similarmaterial, positioned within, and secured to, the outermost largediameter end 101 of the speaker cone 100 with the decorative cover 106abutting the dust cover/support at their respective midpoints; and vii)and annular spider 108 having a corrugated cross section wherein thedepth of the corrugations progressively increase from the innerperiphery towards the outer periphery with the spider 108 being securedat its innermost periphery to the outer surface of the voice coil former102 and at its outer periphery to the frame or cage 90 of the apparatus.

Thus, the arrangement is such that when positive or negative voltagelevels are output from the tracking downconvertor drive amplifier (notshown in FIGS. 2-5, but described in greater detail below in connectionwith FIGS. 13, 14A, 14B and 30-32)—which is capable of delivering 2,700watts rms to a nominal 4 ohm resistive load and swinging 104 voltsrms—and applied to the voice coil 104, current flows through the voicecoil 104 creating magnetic fields around the voice coil. These voicecoil magnetic fields interact with the magnetic field of the magnet 94,causing the voice coil former 102, voice coil 104, speaker cone 100,dust cover 105, surround 78′, decorative cover 106 and spider 108 tomove in an axial direction—e.g., in an outward axial PUSH direction whenpositive voltage levels are output from the tracking downconvertor driveamplifier; and, in an inward axial PULL direction when negative voltagelevels are output from the tracking downconvertor drive amplifier.

Thus, the movable voice coil former 102 and voice coil 104 move axiallywithin the magnetic gap 99 between the annular pole piece 98 and theannular upper spacer 92 with a PUSH/PULL movement dependent upon thepolarity of the voltage applied to, and the current flow in, the voicecoil 104. Since the voice coil former 102 and voice coil 104 reciprocateaxially within the magnetic gap 99—i.e., move to the left and to theright as viewed in FIGS. 3 and 5—the speaker cone 100 attached to theright hand end of the voice coil former 102 as viewed in FIGS. 3 and 5reciprocates axially with the voice coil 104 and voice coil former 102.Such reciprocating movement is permitted because of the resilient natureand shapes of: i) the surround 78′—which is self supporting andsemi-rigid; and ii), the spider 108, which together represent the solesuspension mechanisms for the movable components of the voice coildriven woofer 54. Moreover, the surround 78′ and spider 108—butparticularly the surround 78′—are designed so as to be capable of: i)permitting a peak-to-peak stroke of the movable driver components of upto about 2.5″; ii) resisting or standing off internal box pressureranging up to about 3 lbs/in²—in the exemplary embodiment of theinvention, from about 1.5 lbs/in² to about 3 lbs/in² (an internal boxpressure which, when applied to a typical 8″ diameter speaker cone 100,translates to a force of approximately 150 lbs. applied to the speakercone (100); and iii), simultaneously supporting and stabilizing themoveable driver components on the longitudinal axis passing through themagnetic gap 99 without significant or meaningful wobble.

It will further be noted that an accelerometer 109 is mounted in thespeaker cone (100) on the end of the voice coil former 102. Theaccelerometer 109 serves to sense the movement of the movable componentsof the voice coil driven woofer 54 and any movement distortion, withsignals representative of such movement and any such distortions beingconveyed to the processing circuitry discussed hereinafter.

Referring next to FIG. 4, an isometric view of the exemplary voice coilformer 102 having a voice coil 104 wound thereabout has been depicted.It will be noted that electrical leads 110, 111 are coupled to the voicecoil 104 and project outwardly from the voice coil former 102, whichleads 110, 111 are electrically coupled to tinsel leads 112 extendingfrom the frame 90 to the speaker cone 100 as shown in FIG. 3. In thepractice of the exemplary form of the invention herein illustrated anddescribed, the voice coil 104 is preferably a four layer winding havingan internal diameter of approximately 3.25″ and an overall windinglength of approximately 2″.

Turning next to FIGS. 6 and 7 conjointly, details of the surround 78 forthe mass driven woofer 52, which surround embodies features of, and ismade in accordance with, the present invention, have been illustrated.As here shown, it will be noted that the exemplary surround 78 employedin a subwoofer having a speaker cone 100 with an effective 8″ diameteris approximately 9.9 inches in diameter. The outer peripheral flange 79of the surround 78 is approximately 0.3875 inches wide terminating atits inner edge in a half round or edgeroll 80 having an outside diameter(“O.D.”) of approximately 1.5″. The surround 78 is preferably ofsubstantially uniform thickness throughout; and, is preferably on theorder of about 0.1 inches in thickness or greater. As previouslyindicated, the only difference between the surround 78 shown in FIGS. 6and 7 used with the mass driven woofer 52 and the surround 78′ for thevoice coil driven woofer 54 is the fact that the central flatdisk-shaped portion 82 of the surround 78 has been removed from thesurround 78′ for the voice coil driven woofer 54 as shown in FIG. 8.

The surround 78′ described above is intended for use in supporting aspeaker cone 100 having an effective 8″ diameter which would normally bemounted in a basket-like frame or cage 90 having a diameter ofapproximately 10″. When the surround is intended for use with, forexample, a speaker cone 100 (FIGS. 3 and 5) having an effective 10″diameter and mounted in a basket-like frame or cage 90 having a diameterof approximately 12″, the surround 78′ will have a diameter ofapproximately 11.9″, a uniform thickness on the order of at least 0.14″,or more, an outer peripheral flange 79 approximately 0.3875″ wide, andan edgeroll 80 having an I.D. of approximately 1.5″.

Conventional surrounds are, and have been, typically fabricated from,for example, an expanded cellular polyethylene (“PE”) surround foamsheet which is approximately {fraction (7/16)}″ in thickness and whichis compressed to form a very resilient, compliant suspension memberhaving a thickness of approximately 0.02″. Such conventional prior artsurrounds are very thin and flexible, often having little more rigiditythan rubber gloves; and, consequently, have very little ability to standoff internal pressures within the woofer box 51. However, sinceconventional woofers generally generate internal pressures of only onthe order of about 0.1 lbs/in² to about 0.2 lbs/in², and normally havepeak-to-peak strokes of only 0.4″ to 0.6″, the conventional thin, highlyflexible, compliant prior art surrounds have generally been acceptable.Typically such conventional surrounds will have an outer half roll or“edgeroll” of not more than, and usually less than, one inch indiameter.

As will be described hereinbelow, the mass driven woofer 52 and voicecoil driven woofer 54 of the present invention are driven throughpeak-to-peak excursions up to about 2.5″ as contrasted with conventionalwoofers which typically have peak-to-peak excursions ranging from onlyabout 0.4″ to about 0.6″—i.e., the movable components of the drivers 52,54 of the present invention are driven to excursions ranging from fiveto six times the excursions typically generated in conventionalsubwoofers. Moreover, subwoofers made in accordance with the presentinvention generate internal box pressures up to about 3 lbs/in²—in theexemplary form of the invention, from about 1.5 lbs/in² to about 3lbs/in²—as contrasted with internal box pressures of only 0.1 lbs/in² toabout 0.2 lbs/in² for conventional subwoofers—i.e., the internal boxpressures that must be withstood by the surrounds 78, 78′ of the presentinvention range from fifteen to thirty times greater than the internalpressures generated in conventional subwoofers. Accordingly,conventional surrounds are simply not capable of standing off thepressures generated and/or supporting the movable driver components freeof wobble and in a stable, but axially reciprocable, position whereinthe voice coil former 102 and the voice coil 104 wound thereabout arecapable of moving axially within the magnetic gap 99 through apeak-to-peak stroke of up to about 2.5″ without touching either theannular pole piece 98 or the surrounding magnet/spacer 94/92 structure.

In accordance with one of the important aspects of the presentinvention, the surrounds 78, 78′ of the present invention have beenmodified in two significant respects as compared with conventionalsurrounds. Although made of an expanded synthetic cellular foam such,for example, as an expanded cellular polyethylene (“PE”) surround foamwhich is typically supplied in sheets {fraction (7/16)}″ thick, thefinished surrounds 78, 78′ of the present invention are, for an 8 inchspeaker, preferably a minimum of about 0.1″ in thickness ranging up to0.14″ in thickness or more—i.e., from five to seven times the thicknessof a conventional surround for eight inch and larger conventionalsubwoofers. Secondly, the half round or “edgeroll” 80 of the surrounds78, 78′ employed with the present invention have an outside diameter ofapproximately 1.5″ as contrasted with conventional surrounds whichtypically have an edgeroll of not more than, and usually less than, 1.0″in outside diameter.

In order to carry out this aspect of the invention, and as best shown inFIGS. 9, 10 and 11, the surrounds 78 of FIGS. 6 and 7 are formed in apress, generally indicated at 114, having complementary cooperable maleand female die portions 115, 116 respectively. In one form of theinvention as depicted in FIG. 9, multiple layers 118 a-118 n of anexpanded synthetic cellular foam—such, for example, as an expandedcellular polyethylene (“PE”) surround foam—each approximately {fraction(7/16)}″ thick are positioned in abutting face-to-face relation withinthe female die 116 of the press 114. For an eight inch speaker,typically there will be at least five such layers 118 a-118 e (i.e.,where “n” equals “e” or five) totaling at least 2{fraction (3/16)}″ inaggregate thickness; and, there may be up to seven or more such layerswith each additional layer increasing the aggregate thickness byapproximately {fraction (7/16)}″. Alternatively, where available, asingle sheet 118 of an expanded synthetic cellular foam—e.g., anexpanded cellular polyethylene (“PE”) surround foam having a thicknessof at least 2{fraction (3/16)}″, or more—can be placed within the femaledie 116 as shown in FIG. 10. Of course, where the thickness of theexpanded cellular foam layer(s) exceeds approximately 2{fraction(3/16)}″, the female die member 116 must be modified to accommodate theadditional material and to allow for a uniform thickness of thosefinished surrounds having thicknesses greater than about 0.1″. In eithercase, the male die 115 is then shifted relative to the female die 116 ina suitable press at a temperature of approximately 430° F. andapproximately 80 psi for a period on the order of about forty-five (45)seconds.

Those skilled in the art will, of course, appreciate that the pressure,temperature and time parameters set forth hereinabove can be variedsomewhat without departing from the spirit and scope of the invention asexpressed in the appended claims. However, it has been found thatexcellent results can be obtained on a consistent replicable basiswhere: i) pressure is maintained in the range of from about 60 psi toabout 100 psi with about 80 psi being preferable; ii) temperature ismaintained in the range of about 420° F. to about 450° F.; and iii),time is maintained in the range of from about forty (40) seconds toabout ninety (90) seconds. Surrounds 78, 78′ embodying features of thepresent invention, and made in accordance with the methods of thepresent invention, have been manufactured by Rapid Die & Molding Co.,Inc. of Schiller Park, Ill., to specifications originated and developedby the inventor using tooling proprietary to the inventor.

The process and product parameters for manufacturing conventional singleply surrounds using a single layer of expanded cellular polyethylene(“PE”) surround foam of approximately {fraction (7/16)}″ in thickness toproduce highly resilient compressed surrounds with thicknesses of notmore than about 0.02″ and a half round or “edgeroll” of not more than1.0″ O.D. using an RDM2102 press (without the modifications required forthe practice of the present invention) are proprietary to, and theproperty of, Rapid Die & Molding Co., Inc.; and, no claim is, or willhereafter be, made herein and/or in any future application filed by oron behalf of the inventor which would interfere with Rapid Die & Mold'sexclusive right to use its pre-existing proprietary processes,information and technology; but, such prior processes, information andtechnology may not be modified so as to enable Rapid Die & Mold and/orothers to manufacture surrounds 78, 78′ embodying features of thepresent invention and/or in accordance with the processes of the presentinvention—i.e.,: i) surrounds 78, 78′ employing half rolls or“edgerolls” 80 having diameters of approximately 1.5″; and/or ii),surrounds 78, 78′ having a substantially uniform thickness on the orderof about 0.1″ or greater formed from either; a) multiple layers 118a-118 n of an expanded synthetic cellular foam such, for example, as anexpanded cellular polyethylene (“PE”) surround foam, and/or from othersimilar natural or synthetic materials, aggregating on the order ofapproximately 2{fraction (3/16)}″ thickness or greater prior tocompression; or b), a single layer 118 of such material having aninitial thickness equal to or greater than on the order of approximately2{fraction (3/16)}″. The resulting surround 78, when removed from thepress 114, exhibits the characteristics and dimensions of the surroundas shown in FIGS. 6 and 7 and which has been described hereinabove.

Directing attention now to FIGS. 12A, 12B and 13, an illustrative, butmerely exemplary, overall circuit architecture directly controllingoperation of the voice coil driven woofer 54 (FIGS. 2, 3 and 5)—and,therefore, indirectly controlling operation of the slaved mass drivenwoofer 52 in a manner to be explained in further detail hereinbelow—hasbeen illustrated in highly diagrammatic block-and-line form. Thespecific circuit details for each of those blocks representative ofunique circuitry employed in carrying out the present invention will bedescribed in greater detail below in connection with FIGS. 24 through33; while those blocks which are representative of conventionalelectrical circuitry well known to persons skilled in the art willsimply be indicated to be conventional and will not, therefore, bedescribed herein in further detail since such a description should notbe necessary for persons skilled in the art. Nevertheless, theparticular schematic circuit details, including identification ofelectrical components and values, are fully disclosed in thecomputer-generated size “D” schematic circuit drawings submittedconcurrently with filing of this application as Appendices “A” and “B”and forming part of the file history thereof; although, such Appendicesare not to be printed as part of any Letters Patent(s) issuing herefrom.Those interested in acquiring further information pertaining to suchconventional circuits are, therefore, referred to Appendices “A” and“B”.

Thus, in carrying out the present invention, and as best shown in FIGS.12A and 12B, an audio signal, generally indicated at 120 a, 120 b (FIG.12A), from any suitable signal source is input to the subwoofer 50 ofthe present invention by suitable cable(s) (not shown) plugged into oneor both pairs of input jacks 66, 68 on the rear wall 58 control panel ofthe woofer cabinet 51 as shown in FIG. 1; and, such audio signal ispresented as left and right inputs 120 a, 120 b, respectively, to theInput Buffers 125 as shown in FIG. 12A. The Input Buffers 125 serve twoimportant functions—viz., first they serve to isolate the electronicswithin the subwoofer 50 from the environment outside the subwoofercabinet 51 (FIGS. 1 and 2); but, more importantly, they also serve toalgebraically sum and process the left and right components 120 a, 120 brespectively of the audio signal—i.e., the L+R components and the L−Rcomponents—in such a way that the L+R and the L−R components of theaudio signal are output from the Input Buffers 125 as a composite audiosignal (L+R)+α(L−R), generally indicated at 126 in FIG. 12A, whichretains both the L+R and the L−R components of the audio signal. This isa significant and important advance in subwoofer design; and, isdistinguishable from conventional prior art subwoofers where the L−Rcomponents of the signal are, in effect, destroyed. As a consequence ofretaining both the L+R and the L−R components of the audio signal, theaudio sounds presented to the listeners are characterized by enhancedlife, luster, depth and impact—in effect replicating what the human earhears in a live performance. Specific details of a simplified exemplaryembodiment of the Input Buffers 125 are shown and will be described ingreater detail below in connection with FIG. 24. Moreover, althoughmerely exemplary, a specific detailed circuit arrangement, includingcomponent identities and values, is contained within Appendix “B”submitted concurrently with this Application and forming part of thefile history hereof; and, those persons interested in acquiring suchschematic details are referred to Appendix “B”.

The Input Buffers 125 output a composite audio signal 126 containingboth the L+R and the L−R components of the signal successively to: i) aGround Loop Hum Eliminator 124; ii) a Subsonic Filter 130, iii) an E.Q.Amplifier 131; iv) a Video Contour Controller 132; v) a Phase Amplifier134; vi) a Crossover Control circuit 135; vii) a Volume Control 136;viii) a Line Amplifier 138; ix) an Opto-Coupler 139 (which serves tofurther isolate the electronics within the subwoofer 50 from theenvironment outside the subwoofer cabinet 51); and x), a MasterProtection Circuit 140. The Subsonic Filter 130, E.Q. Amplifier 131,Video Contour Controller 132, Phase Amplifier 134, Crossover Controlcircuit 135, Volume Control 136, Line Amplifier 138 and Opto-Coupler 139are all completely conventional circuits well known to persons skilledin the art and will not be described herein in further detail. Thoseinterested in acquiring more detailed information with regard to suchconventional circuits are referred to Appendix “B”.

The Master Protection Circuit 140 illustrated in block-and-line form inFIGS. 12A and 12B includes: i) an Overshoot Control circuit 141; ii) anExcursion Limiter circuit 142; iii) a Clipping Level circuit 144; andiv), an Impulse Damper 145 for processing the audio signal 126 (audiosignal flows are indicated by “→” in FIGS. 12A and 12B) with theprocessed audio signal 126 being output from the Master ProtectionCircuit 140 by the Impulse Damper 145. Additionally, the MasterProtection Circuit 140 includes: v) a Clipping Eliminator circuit 146;vi) a Low Frequency Auto-Throttle circuit 143; vii) a Manual ThrottleSet circuit 148; viii) a Thermal Integrator circuit 149; and ix), aThermal Integrator Trip circuit 150 for generating control signals(control signal flows are indicated by “→→” in FIGS. 12A and 12B) whichserve to control the audio signal 126 being processed.

Of the foregoing processing and control circuits, the Excursion Limitercircuit 142 (FIGS. 12B and 25), Clipping Level circuit 144 (FIGS. 12Band 27), Thermal Integrator circuit 149 (FIGS. 12B and 27), ThermalIntegrator Trip circuit 150 (FIGS. 12B and 27), Low FrequencyAuto-Throttle circuit 143 (FIGS. 12B and 26), Impulse Damper circuit 145(FIGS. 12B and 27), and Ground Loop Hum Eliminator 124 (FIGS. 12A and33) uniquely contribute to carrying out the present invention and willbe described in greater detail hereinbelow in connection with suchdrawings. Those interested in acquiring further detailed informationabout any or all of those circuits or, for that matter, the OvershootControl circuit 141, Manual Throttle Set circuit 148 and/or ClippingEliminator circuit 146 (each of the latter three circuits are completelyconventional and well known to persons skilled in the art) are referredto Appendix “B”.

In keeping with the invention, the thus processed audio signal outputfrom the Impulse Damper 145 (FIGS. 12B and 27) is presented at the inputport 154 of a Woofer Servo 155 (FIGS. 13 and 28). The Woofer Servo 155receives: i) the partially processed audio signal 126 output from theImpulse Damper 145; and ii), a feedback signal via leads 156, 158 fromthe accelerometer 109 installed in the voice coil driven woofer 54(FIGS. 3 and 13). The accelerometer 109 is mounted on the voice coilformer 102 in the driver depicted in FIG. 3; and, is used to sense themotion of the driver 54. If the driver's motion is non-linear—i.e.,distorted—the signal output by the accelerometer 109 will be a replicaor exact analog of that distortion. For example, if the audio signal 120a, 120 b input to the Input Buffers 125 (FIGS. 12A and 24) of thesubwoofer 50 is undistorted, and the voice coil driven driver 54 ismoving in a distorted fashion, the output of the accelerometer 109 willalso be distorted and fed back to the Woofer Servo 155 (FIGS. 13 and 28)where it is combined with the original processed input audio signal 126output from the Impulse Damper (FIGS. 12B and 27). The original inputaudio signal 126 is then modified in an inverted fashion with respect tothe distortion sensed; and, the result is that the voice coil drivendriver 54 receives a non-linear drive signal in such a way that thedriver's motion is linear and nondistorted—i.e., the inverted non-lineardistorted signal impressed on the original non-distorted or linear inputaudio signal 126 output from the Impulse Damper 145 (FIGS. 12B and 27)serves to substantially cancel any non-linear distortions in movement ofthe voice coil driven woofer 54 which are sensed by the accelerometer109 and are input to the Woofer Servo 155 via leads 156, 158. Anexemplary embodiment of the Woofer Servo 155 is depicted in FIG. 28 andwill be described below. Specific circuit details and component valuesfor the Woofer Servo 155 are contained in Appendix “B”.

The audio signal which is output from the Woofer Servo 155 is, as bestshown in FIG. 13, input to a Buffer 160 and, from the Buffer 160, to aDiode Steering Network 165. The Diode Steering Network 165 is utilizedso as to ensure that the audio signal is processed into itspositive-going components and its negative-going components, with thepositive-going components of the audio signal being presented to a (+)Tracking Downconvertor Power Supply 170, the negative-going audio signalcomponents being presented to a (−) Tracking Downconvertor Power Supply180, and the composite audio signal being presented to the DriverAmplifier 190. More specifically, those skilled in the art willappreciate that audio signals contain both positive voltage swings andnegative voltage swings. Amplifiers, unless they are biased in Class Aoperation, cannot reproduce both the positive and negative informationwithout crossover distortion. Various solutions to this problem havebeen developed, such as Class AB biasing (a high heat, relatively lowefficiency, solution).

The present invention solves this problem by “steering” the positivecomponents of the audio signal to the (+) Tracking Downconverter PowerSupply 170 while the negative voltage components are steered to the (−)Tracking Downconvertor Power Supply 180. The (+) and (−) TrackingDownconvertor Power Supplies 170, 180 respectively output the (+)v.output signals and the (−)v. output signals to the Driver Amplifier 190which also receives the composite audio signal from the Diode SteeringNetwork 165. As a consequence of this arrangement, the Driver Amplifier190 is enabled to deliver amplified positive voltage levels to the voicecoil 104 during positive swings of the audio signal; and, thus drive thevoice coil driven woofer 54 through a PUSH stroke of up to about 1.25″.Similarly, the (−)v. signals input to the Driver Amplifier 190 enablethe latter to feed amplified negative voltage levels to the voice coil104 during the negative-going portions of the audio signal, thus drivingthe voice coil driven woofer 54 through a PULL stroke of up to about1.25″, with the total peak-to-peak PUSH/PULL stroke being up to about2.5″.

As previously discussed, the output of the Diode Steering Network 165(FIGS. 13 and 29) is conveyed to the (+) and (−) Tracking DownconverterPower Supplies 170, 180. In keeping with the invention, and as will bediscussed below in greater detail, the (+) and (−) TrackingDownconverter Power Supplies 170, 180 are capable of supplying largeamounts of current and, therefore, large amounts of power to the DriverAmplifier 190. Indeed, the (+) and (−) Tracking Downconvertor PowerSupplies 170, 180, together with the Driver Amplifier 190, define atracking downconvertor drive amplifier which, though it weighs onlyabout 11 oz., is capable of delivering 2,700 watts rms output power intothe 3.3 ohm resistive load—i.e., the impedance of the voice coil 104(herein elsewhere referred to as a “nominal 4 ohm resistive load”)—andof swinging 104 volts rms. The ability of the (+) and (−) TrackingDownconvertor Power Supplies 170, 180 and Driver Amplifier 190 todeliver large amounts of power provides many advantages. For example, itallows the cabinet 51 (FIGS. 1 and 2) to be extremely small becauselarge amounts of power can be provided to the voice coil driven driver54 to overcome the pressures created by small cabinet volumes. Further,because the pressures created by a small cabinet volume can be overcome,it is possible to utilize drivers 52, 54 with much longer strokes thanused in the prior art. Thus, in the illustrative embodiment of thepresent invention, the cabinet 51 can have sides having a length ofapproximately 11″, drivers 52, 54 having a diameter of approximately 8″,and maximum peak-to-peak strokes of approximately 2.5″. Such a driver52, 54 could not be used by prior art subwoofers because the powernecessitated by such a combination could not be provided. The details ofan exemplary embodiment of the (+) and (−) Tracking Downconverter PowerSupplies 170, 180 will be discussed below—first in connection with theblock-and-line drawing in FIGS. 14A, 14B and subsequently in greaterdetail in connection with FIGS. 30 and 31A-31C; while details of theDriver Amplifier 190 will be discussed below in connection with FIGS.13, 14A, 14B, 30 and 32.

Turning now to FIGS. 14A, 14B, exemplary (+) and Tracking DownconverterPower Supplies suitable for use with the present invention have beenillustrated at 170, 180, respectively, in block-and-line form. A powersupply somewhat similar to those utilized in the exemplary embodiment ofthe present invention is disclosed in U.S. Pat. No. 4,218,660, issuedAug. 19, 1980 to Robert W. Carver; and, the disclosure contained in thespecification and drawings of the aforesaid U.S. Pat. No. 4,128,660 ishereby incorporated by reference. The (+) and (−) Tracking DownconvertorPower Supplies 170, 180 of the present invention regulate the amount ofcurrent delivered to the voice coil 104 of the voice coil drivensubwoofer 54 (FIGS. 2, 3 and 5) by tracking the audio signal to beamplified and comparing the magnitude of that signal to the signalactually being amplified. The exemplary (+) and (−) TrackingDownconvertor Power Supplies 170, 180 include: i) a common PulseGenerator 200; and ii), a common Square Wave-To-Triangular WaveConverter 201; while each of the (+) and (−) Tracking DownconvertorPower Supplies 170, 180 includes its own: iii) Ramp Time Modulator 171,181; iv) Switch 172, 182; v) Power Output Section, generally indicatedat 174, 184, including an inductor L1, L2; vi) Power Output Feedbackcircuit 175, 185; and vii), Comparator 176, 186 which receives inputsignals from the Diode Steering Network 165 (FIGS. 13 and 29) and thePower Output Feedback circuit 175, 185 (FIGS. 14A, 14B). The Comparators176, 186 compare the two input signals, and generate control signalswhich are transmitted to respective ones of the Ramp Time Modulators171, 181.

In order to permit operation of the electronic circuits employed in thesubwoofer 50 (FIG. 1) of the present invention, and as previouslyindicated in connection with the description of FIG. 1, power is derivedfrom any suitable and conventional A.C. source (not shown) via an A.C.outlet plug 71 and A.C. power line 72. As best shown in FIG. 14A, A.C.power line 72 is coupled to an Input Power Supply 204 comprising a fullwave voltage doubler having a first pair of diodes D1, D2 coupled inparallel and a second pair of diodes D3, D4 also coupled in parallel.The A.C. input power line 72 is coupled via diodes D1, D2 to thenegative end of a capacitor C1, while also being coupled via diodes D3,D4 to the positive end of a second capacitor C2. Thus, the arrangementis such that when the incoming A.C. signal on A.C. power line 72 ispositive, diodes D1 and D2 are turned OFF, while diodes D3 and D4 areturned ON. Therefore, the positive portion of the A.C. signal flowsthrough diodes D3, D4 and charges up capacitor C2 to +160 volts.Conversely, when the A.C. signal on the A.C. power line 72 is negative,diodes D3, D4 are turned OFF while diodes D1 and D2 are turned ON,permitting the negative portion of the A.C. signal to charge upcapacitor C1 to −160 volts. Discharge of capacitor C2 allows +160 voltsto be delivered to Switch 172 in the (+) Tracking Downconvertor PowerSupply 170 (FIG. 14A); while discharge of capacitor C1 allows −160 voltsto be delivered to Switch 182 in the (−) Tracking Downconvertor PowerSupply 180 (FIGS. 14A and 14B).

The power delivered to the driver of the voice coil driven woofer 54 bythe inductors L1, L2 in respective ones of the Power Output Sections174, 184 of the (+) and (−) Tracking Downconvertor Power Supplies 170,180 is controlled by controlling the time within which the Switches 172,182 in the respective Downconvertors 170, 180 are CLOSED for eachcurrent pulse. This is accomplished by tracking the audio signals whichare to be amplified by the Driver Amplifier 190; and, comparing thesetracked signals to the voltage imposed across the Driver Amplifier 190.This produces a control signal which controls the duration of eachcurrent pulse delivered to the respective inductors L1, L2. In otherwords, on the assumption that the Switches 172, 182 are being opened andclosed at a frequency of 100 Kilohertz, the duration of each time periodwould be 10 microseconds. During those time periods where the powerrequirements of the Driver Amplifier 190 are high, then during each 10microsecond time period, a respective one of the Switches 172, 182 willbe CLOSED (dependent upon whether the polarity of the audio signal isthen positive or negative) for a relatively large fraction of thattime—e.g., for about 5 to about 7 microseconds. On the other hand, whenpower requirements of the Driver Amplifier 190 are relatively low, therespective Switches 172, 182 will be CLOSED in each time period for amuch shorter duration.

As discussed above, the audio signal containing the low frequencyinformation which is to be reproduced by the subwoofer 50 ultimatelyenters the Diode Steering Network 165 (FIGS. 13 and 29). A portion ofsuch an audio signal is graphically indicated in FIG. 15 at 205. Notethat the audio signal has both positive and negative portions 206, 208,respectively, with the positive portions 206 being represented as beingabove the abscissa in FIG. 15 and the negative portions 208 beingrepresented below the abscissa. The Diode Steering Network 165 producesan output where the negative portions 208 of the audio signal aresteered to the (−) Tracking Downconvertor Power Supply 180, andsimilarly, the positive portions 206 of the audio signal are steered tothe (+) Tracking Downconvertor Power Supply 170. The output of the DiodeSteering Network 165 is graphically depicted at 209 in FIG. 16 forpositive-going signals.

The output of the Diode Steering Network 165 is then directed to theComparator 176 in, for example, the (+) Tracking Downconvertor PowerSupply 170. The Power Output Feedback circuit 175, which is responsiveto the voltage impressed across the power input terminals of the DriverAmplifier 190, transmits a voltage generally proportional to the voltageat the power input terminals of the Driver Amplifier 190 as a secondinput to the Comparator 176. The Comparator 176 then “compares” thesignal input from the Diode Steering Network 165 and the signal inputfrom the Power Output Feedback circuit 175 to produce a control signal214 (FIG. 19) generally proportional to the difference between the twoinputs.

Referring next to FIG. 17, it will be observed that the two inputsignals to the Comparator 176 have been graphically depicted at210—i.e., a solid line representing the signal input from the PowerOutput Feedback circuit 175—and a broken line 211 representing thesignal input from the Diode Steering Network 165. It will further benoted upon comparison of FIGS. 17 and 18 that there is a relationshipbetween: i) the magnitude of the signal 211 from the Diode SteeringNetwork 165; and ii), the difference between the signal 211 from theDiode Steering Network 165 and the signal 210 from the Power OutputFeedback circuit 175 in that the increment of increase and thedifference between the two signals 210, 211 increase generallyproportionally to the magnitude of the signal 211 from the DiodeSteering Network 165 as represented by the broken line 212 in FIG. 18.For purposes of illustration, this difference has been exaggeratedsomewhat in FIG. 18 from what the actual values may be. The controlsignal 214, which is the output of the Comparator 176, has beengraphically illustrated in FIG. 19. It can be seen that this controlsignal 214 generally corresponds to the increment of increase ordecrease in the difference between the two input signals illustrated inFIGS. 17 and 18. Thus, the control signal 214 is used to control theduration of the regularly timed current pulses in the inductor L1.

In keeping with the broad objectives of the present invention, the PulseGenerator 200 associated with the (+) and (−) Tracking DownconverterPower Supplies 170, 180 illustrated in FIGS. 14A, 14B functions togenerate a pulsed wave of a constant voltage as indicated at 215 in FIG.20—i.e., a wave where the gaps between the pulses are of approximatelythe same duration as the pulses themselves. The pulses are, in turn, ofthe same frequency as the desired current pulses for the respectiveinductors L1, L2. In the particular embodiment described herein, wherethe frequency of the current pulses in the inductors is 100 Kilohertz,the output from the Pulse Generator 200 would be of the same frequency.

The output pulse wave 215 (FIG. 20) from the Pulse Generator 200 isdirected to the Square Wave-To-Triangular Wave Converter 201. Thisserves to convert the wave form 215 of FIG. 20 to a wave form 216 suchas shown in FIG. 21 where each pulse has the configuration of anisosceles triangle; and, where, during the duration of each pulse, thevoltage climbs at a substantially constant rate to a peak at the middleof the pulse, and then declines at a constant rate through the latterhalf of the pulse.

The output wave form 216 from the Square Wave-To-Triangular WaveConverter 201 is then transmitted to the Ramp Time Modulators 171, 181of the respective (+) and (−) Tracking Downconvertor Power Supplies 170,180. As previously described, the Ramp Time Modulators 171, 181 alsoreceive the control signal 214 from their respective Comparators 176,186. This is illustrated in FIG. 21 by graphically representing aportion of the control signal 214 from the Comparators 176, 186 inbroken lines superimposed over the triangular wave form 216 output fromthe Square Wave-To-Triangular Wave Converter 201. As shown in FIG. 21,that portion of the control signal 214 is increasing in magnitude. Forpurposes of illustration, the slope representing the rate of increase ofthe control signal 214 may be exaggerated to some extent.

The output of the Ramp Time Modulators 171, 181 is illustrated in FIG.22 as a constant voltage pulse signal 218 having the same frequency asthat of the Pulse Generator 200. The duration of each pulse is directlyproportional to the duration of the bottom portion of the triangularwave form 216 depicted in FIG. 21. Thus, it can be appreciated bycomparing the duration of the pulses of FIG. 22 with the slope of thecontrol signal 214 as indicated in the broken lines of FIG. 21, that theduration of the pulses shown in FIG. 22 are proportional to themagnitude of the control signal 214 as shown in FIG. 21.

The voltage pulse signals 218 depicted in FIG. 22 are output from theRamp Time Modulators 171, 181; and, are used to open and closerespective ones of the Switches 172, 182 in such a manner that theSwitches are CLOSED during the duration of each of the pulses depictedin FIG. 22. The manner in which the voltage pulses 218 from the RampTime Modulators 171, 181 act on respective ones of the Switches 172, 182to cause current pulses 219 in the inductors L1, L2 is illustrated inFIG. 23. Thus, it can be seen that a voltage pulse of relatively shortduration as indicated at 218 a in FIG. 22 produces a correspondingcurrent pulse 219 a (FIG. 23) of relatively small amplitude, since thecurrent has such a very short time period to build up or “ramp up”. Itcan be seen in FIG. 23 that as the voltage pulses 218 of FIG. 22increase in duration, the amplitude of the current pulses 219 outputfrom the Switches 172, 182 and routed to respective ones of theinductors L1, L2 increase correspondingly. Thus, the voltage pulse 218 bwhich has the longest duration of the voltage pulses 218 shown in FIG.22, produces a current pulse 219 b of the largest amplitude of thoseshown in FIG. 23.

Those skilled in the art will, of course, appreciate that the foregoingdescription of the operation of one of the (+) and (−) TrackingDownconvertor Power Supplies 170, 180 is equally applicable to theother.

Having the foregoing in mind, a brief overview of the operation of the(+) and (−) Tracking Downconvertor Power Supplies 170, 180 will be setforth hereinbelow in terms of the block-and-line diagrams depicted inFIGS. 13, 14A and 14B. As previously indicated, the subwoofer 50 of thepresent invention is provided with electrical power from any suitableA.C. source (not shown) via an A.C. outlet plug 71 (FIGS. 1 and 14A). Inthe United States, the A.C. source will comprise and alternating currentsource of 110 to 120 volts and 60 cycles per second. Other countrieshave somewhat different systems. However, the concepts discussed hereincan be adapted by one of ordinary skill in the art to electrical systemsof other countries without departing from the spirit and scope of thepresent invention. The current from the A.C. source is rectified by thefull wave voltage doubler in the Input Power Supply 204 in the mannerdescribed above to convert the A.C. current to direct current and allowdelivery of +160 volts and −160 volts to respective ones of the Switches172, 182 in the (+) and (−) Tracking Downconvertor Power Supplies 170,180.

Referring to FIGS. 14A, 14B it will be noted that the currentpulses—e.g., pulses graphically depicted at 219 in FIG. 23—output fromthe Switches 172, 182 are coupled to respective ones of inductors L1, L2and to respective ones of diodes D5, D6. Diode D5 has its positiveterminal connected to ground in the (+) Tracking Downconvertor PowerSupply 170, while the negative terminal of Diode D6 is connected toground in the (−) Tracking Downconvertor Power Supply 180. The diodesD5, D6 complete the circuit path so that current may continue to flow inthe inductors L1, L2 and into the load during OFF time periods of therespective Switches 172, 182.

The arrangement is such that when an audio signal is presented at theinput terminals 66 and/or 68 (FIGS. 1 and 12A) of the subwoofer 50 foraudible reproduction, the signal is presented to the Input Buffers 125;and, is then passed successively to and through the Ground Loop HumEliminator 124, Subsonic Filter 130, E.Q. Amplifier 131, Video ContourController 132, Phase Amplifier 134, Crossover circuit 135, VolumeControl 136, Line Amplifier 138, Opto-Coupler 139 and the MasterProtection Circuit 140 in the manner previously described so as toprocess the audio signal and extract the low frequency information thatwill be audibly reproduced. The Impulse Damper 145 in the MasterProtection Circuit 140 then outputs the low frequency signal to theWoofer Servo 155 (FIGS. 13 and 28). The Woofer Servo 155 utilizes thefeedback signal on leads 156, 158 from the accelerometer 109 (FIGS. 3and 13) associated with the voice coil driven woofer 54 (FIG. 3) toservo the audio signal, with such feedback signal being conveyed fromthe voice coil driven woofer 54 to the Woofer Servo 155 as shown in FIG.13.

Thereafter, the low frequency audio signal which has been servoed ispresented to the Diode Steering Network 165 which performs severalfunctions. For example, and as discussed above, the Diode SteeringNetwork 165 produces a signal output wherein the negative portions ofthe audio signal are directed to the (−) Tracking Downconvertor PowerSupply 180, and where the positive portions of the audio signal aredirected to the (+) Tracking Downconvertor Power Supply 170. For anexample of this, see FIGS. 15 and 16, and the above description relatingthereto.

In keeping with this aspect of the present invention, the Diode SteeringNetwork 165 ensures that the positive-going and negative-going audiosignals are amplified at the proper time. Thus, when the subwoofer 50receives an audio signal to reproduce, the Diode Steering Network 165transmits an enabling signal to the Driver Amplifier 190 via line 166for both positive and negative swings of the audio signal. The DiodeSteering Network 165 also sends the positive-going portions and thenegative-going portions of the audio signal to respective ones of the(+) and (−) Tracking Downconverter Power Supplies 170, 180 viarespective ones of lines 168, 169 in the manner previously describedabove with reference to FIGS. 13, 14A and 14B.

Since upon initial start up there is no voltage generated at the outputof the Power Output Sections 174, 184 of either the (+) or the (−)Tracking Downconvertor Power Supplies 170, 180, the feedback signalprovided by the respective Power Output Feedback circuits 175, 185 arezero or substantially zero. Accordingly, at start up, the Comparators176, 186 generate a rather strong output signal 214 (FIG. 19) which istransmitted to respective ones of the Ramp Time Modulators 171, 181 inthe (+) and (−) Tracking Downconvertor Power Supplies 170, 180. The RampTime Modulators 171, 181, in turn, transmit current pulses 219 (FIG. 23)of the desired frequency to respective ones of the electronic Switches172, 182, with these current pulses 219 being of a maximum duration. Inother words, the Switches 172, 182 continue to turn ON and OFF at thesame frequency; but, the duration of the ON periods is at a maximum.Accordingly, the current pulses 219 (FIG. 23) passing through theinductors L1, L2 ramp up to a maximum amperage; and, therefore, deliverfull power to the Driver Amplifier 190. Within a very short period oftime (i.e., about 200 microseconds), the current pulses 219 transmittedto the Driver Amplifier 190 build up to their proper operating level.

At this time, the Power Output Feedback circuits 175, 185 (FIG. 14)transmit to their respective Comparators 176, 186 an output signalrelated to the voltage level applied to the Driver Amplifier 190.Thereafter, the Comparators 176, 186 continue to provide theirrespective Ramp Time Modulators 171, 181 with a control signal 214 (FIG.19) related to the power requirements of the Driver Amplifier 190indicating that the amplitude of the audio signal is increasing; and,consequently, there is a greater disparity between this audio relatedsignal and the signal exiting from the Power Output Feedback circuits175, 185, causing the strength of the control signal 214 beingtransmitted to the Ramp Time Modulators 171, 181 to increase inmagnitude. This, in turn, causes the current pulses 219 (FIG. 23) beingtransmitted through the respective inductors L1, L2 in the Power OutputSections 174, 184 to increase in duration so as to deliver more power tothe Driver Amplifier 190; and, thus raise the average voltage suppliedat the inductors' L1, L2 respective output terminals 220, 221. On theother hand, when the amplitude of the audio signal is declining, therespective Comparators 176, 186 detect that the difference in the signalbetween the Diode Steering Network 165 and the signals from the PowerOutput Feedback circuits 175, 185 are smaller.

Therefore, the control signals 214 (FIG. 19) transmitted by theComparators 175, 185 to their respective Ramp Time Modulators 171, 181will be at a lower voltage level. This shortens the duration of thecurrent pulses through the respective inductors L1, L2, causing lesspower to be delivered to the Driver Amplifier 190.

Those skilled in the art will readily appreciate from the foregoingdescription that the Comparators 176, 186 will, in effect, “track” theaudio signal to maintain the voltage level impressed upon the outputterminals 220, 221 of the Power Output Sections 174, 184 and which isbeing routed to the Driver Amplifier 190 so that the voltage level isvaried in such a manner that it remains only moderately above the powerrequirements of the Driver Amplifier 190. In actual practice, there isgenerally a voltage drop across the output transistors Q1, Q2 of theDriver Amplifier 190 (FIG. 32) of approximately six volts (6 v.).

Contributing to the small size of the subwoofer 50 (FIG. 1) of thepresent invention is the fact that the (+) and (−) TrackingDownconvertor Power Supplies 170, 180 (FIGS. 13, 14A, 14B and 31A-31C)do not require massive storage capacitors as do the power supplies usedin prior art subwoofers. Because the (+) and (−) Tracking DownconvertorPower Supplies 170, 180 employed with the present invention can deliverlarge amounts of power to the Driver Amplifier 190 so quickly, only asmall amount of power need be held in reserve for sudden increases inthe power demanded by the audio signal. Such sudden increases might, forexample, be caused by a musical or other audio transient such as a louddrum beat or a film special effect such as an explosion.

Because the (+) and (−) Tracking Downconvertor Power Supplies 170, 180used in the subwoofer 50 of the present invention react so quickly totransients, only relatively small storage capacitors C3, C4—viz., 6.8microfarad capacitors rather than the 10,000 microfarad capacitorstypically used in the prior art—are needed for supplying the powernecessitated by a rapid increase in the power requirements of the DriverAmplifier 190. The reason for this is that the power pulses 219 (FIG.23) through the respective inductors L1, L2 are of such high frequency,and the response time of the respective inductors L1, L2 to suchincreases in power pulse duration (and, thus, the corresponding increasein power supplied) so fast, that the inductors L1, L2 can respond in amatter of a fraction of a millisecond to begin delivering full power tothe Driver Amplifier 190. Thus, large 10,000 microfarad storagecapacitors such as typically used in the prior art for supplying powerfor transients are not necessary. Since smaller storage capacitors C3,C4 (FIG. 31) can be used, the cabinet 51 of the subwoofer 50 (FIG. 1)can be made significantly smaller than the cabinets of prior artsubwoofers.

Another advantage provided by the subwoofer 50 of the operationalamplifier OP6 in the Clipping Level circuit 144 as best shown in FIG.27. The Clipping Level circuit 144 serves to clip off the peak portionsof the composite audio signal 126 when the signal is too large. Suchclipping occurs only during the short time period necessary for theExcursion Limiter 142 to clamp the signal and reduce the gain, at whichpoint the composite audio signal 126 no longer requires clipping. Thisrequires only a very short time period; and, consequently, when theClipping Level circuit 144 is functioning to clip the extremely highpeaks in the composite audio signal 126, clipping occurs quickly enoughthat it is not audible to the ear. Resistors R23, R24 serve to set thegain of operational amplifier OP6.

The composite audio signal 126 output from the operational amplifier OP6in the Clipping Level circuit 144 is next conveyed to a Manual ThrottleSet circuit 148 (FIG. 27) which functions to set the value or magnitudeof the audio signal. To accomplish this, the Manual Throttle Set circuit144 includes resistors R25, R26 which form a voltage divider that isfactory preset to provide a predetermined output voltage level at thejunction 151 of the voltage divider R25, R26. To ensure that the ,Manual Throttle Set circuit 148 is frequency dependent, a capacitor C10is provided in parallel with resistor R26.

In order to protect the subwoofer 50 when it gets too hot, the voltagelevel at the junction 151 of the Manual present invention is that thetracking downconvertor drive amplifier therein is very efficient whencompared to amplifiers used in prior art subwoofers. Thus, a typicalprior art amplifier (not shown) used in a conventional prior artsubwoofer requires the use of large heat sinks to dissipate the heatgenerated by the output transistors. The reason for this has to do withconventional amplifier design. More specifically, in conventionalamplifiers of similar power as the invention, the rail voltages wouldgenerally be on the order of 160 volts, leading to thermal dissipationroughly an order of magnitude greater than achieved with the presentinvention. When the conventional amplifier is driving the load—i.e., thedriver of the subwoofer—the amplifier only uses the voltage required bythe driver to produce the appropriate audio volume. If that voltage isless than the voltage provided by the power supply—which it almostalways will be—the remainder of that voltage must be dissipated in theoutput transistors. Thus, if the audio signal requires that the driverbe driven with 30 volts, the remaining 130 volts multiplied by the loadcurrent must be dissipated in the form of heat by the outputtransistors. If a transistor is conducting ten amperes of current, thetransistor is dissipating 1,300 watts of power in the form of heat. Toavoid failure of the output transistors, they must be mounted on largeheat sinks which aid in the heat dissipation. A further problem,however, is that most output transistors are rated at only two-hundredwatts. Consequently, the output of these devices will be currentlimited. This will, therefore, require the use of many outputtransistors, each requiring a large heat sink and, therefore, the sizeof the subwoofer will inherently be substantially increased.

In contrast to prior art subwoofers, the outputs of the (+) and (−)Tracking Downconverter Power Supplies 170, 180 are fixed at a much lowervoltage than the power supplies used in the prior art. For example, inthe exemplary embodiment of the subwoofer 50 of the present invention,the output of each of the (+) and (−) Tracking Downconvertor PowerSupplies 170, 180 is maintained at six volts above the voltage requiredby the Driver Amplifier 190. Thus, when no audio signal is beingamplified, only six volts appears across the output transistors of theDriver Amplifier 190 (FIG. 32). Further, using the example from above,if the driver of the voice coil driven woofer 54 of the presentinvention requires 30 volts to produce the desired volume of sound, the(+) and (−) Tracking Downconvertor Power Supplies 170, 180 will outputonly thirty-six volts. Thus, the output transistors (FIG. 31) used inDriver Amplifier 190 of the present invention will still have todissipate only six volts (6 v.) times the load current. Because typicaloutput transistors can dissipate 200 watts, each of the outputtransistors Q1, Q2, can, theoretically, output over 20 amperes ofcurrent. In reality, typical 200 watt output transistors can output onlyapproximately 3 amperes of current without failure under the sameconditions. Thus, at a maximum, the output transistors used in theDriver Amplifier 190 (FIG. 32) will have to dissipate only approximately80 watts of power as heat. Because of this substantially reduced powerdissipation in the output transistors Q1, Q2, the subwoofer 50 of thepresent invention does not require large eat sinks as do prior artsubwoofers. This further contributes to the reduced size of he subwoofer(FIG. 1) of the present invention.

In carrying out one of the important aspects of the present invention,provision is made for: i) isolating the left and right components of theaudio signal being processed from the external environment; and ii), atthe same time, summing the left and right channels of the audio inputsignal at different decibel (“dB”) levels (rather than at the same dBlevels which would effectively produce a monaural audio output where theL−R component of the audio signal is effectively cancelled and lost),thereby retaining the L−R component of the audio signal representing thestereo sound field which serves to substantially enhance the life,luster, depth and impact of the audio sound for the listener. Thisrepresents a significant advance over conventional subwoofer designswherein the L+R and L−R components are summed to monaural with equalcontributions from both the left and right channel inputs, effectivelycanceling the L−R component of the signal and retaining only the L+Rcomponent which represents the monaural component of the signal asdetermined at points substantially equidistant from the left and rightspeakers.

To accomplish this, and as best illustrated by reference to FIGS. 12Aand 24 conjointly (see, also, Appendix B), the left and right components120 a, 120 b, respectively, of the audio signal input at the left andright input jacks 66 and/or 68 (FIGS. 1 and 12A) are applied torespective ones of the input terminals 128, 129 of the Input Buffers125. The Input Buffers 125 include a pair of operational amplifiers 20OP1, OP2 wherein the left audio signal component 120 a is applied to thepositive input port of operational amplifier OP1, while the right audiosignal component 120 b is simultaneously applied to the positive port ofthe operational amplifier OP2. Operational amplifiers OP1, OP2 aresimply unity gain amplifiers termed “buffers”.

Resistors R1, R2 comprise isolation resistors which serve to protectoperational amplifier OP1, while resistors R3, R4 comprise isolationresistors protecting operational amplifier OP2. The left audio signal120 a output from operational amplifier OP1 and the right audio signal120 b output from operational amplifier OP2 are then summed together byresistors R5, R6 to produce a single composite audio signal 126 which isdefined as:

(L+R)+α(L−R)  [5]

where α is a constant representative of the difference in resistancevalues for resistor R5 (680 ohms) and R6 (1,600 ohms). Because of thisarrangement, the composite audio signal 126 output from the InputBuffers 125 retains the stereo sound field represented by the L−Rcomponents of the audio signal—thereby substantially enhancing thesolidity and realism of the audio sound produced by the subwoofer 50.

Of course, those skilled in the art will appreciate that the values ofresistors R5 (680 ohms) and R6 (1.6 K) can be reversed—i.e., resistor R5can be a 1.6 K resistor while resistor R6 can be a 680 ohmresistor—without departing from the spirit and scope of the invention asexpressed in the appended claims, in which case, the single compositeaudio signal 126 will be defined as:

α(L+R)+(L−R)  [6]

In either case, or, for that matter, in cases where the values of thetwo resistors R5, R6 are other than 680 ohms and/or 1,600 ohms, providedonly that they are significantly different, the left and right channelsof the audio input signal will be summed at different dB levels, therebyproducing the desired results—viz., outputting a composite audio signal126 that retains both the (L+R) and (L−R) components of the audio inputsignal.

The composite audio signal 126—viz., either the signal (L+R)+α(L−R) orthe signal α(L+R)+(L−R)—produced in accordance with one of the importantfeatures of the present invention is then fed through a Ground Loop HumEliminator 124 (FIGS. 12A and 33) embodying one of the importantfeatures of the important features of the present invention and,thereafter successfully through a series of signal processing and/orcontrol circuits which are entirely conventional and need not bedescribed in detail beyond the block diagrammatic description containedin FIGS. 12A and 12B. Those interested in more specific details of suchconventional circuit blocks are referred to Appendix B. Suffice it tosay for purposes of the present description that the composite audiosignal 126 output from the Input Buffers 125 and the Ground Loop HumEliminator 124 is successively conveyed through the followingconventional circuits depicted in block form in FIGS. 12A and 12B:

1) A Subsonic Filter 130 which serves to strip the composite audiosignal 126 of unwanted, very low frequency, inaudible signals thatwould, in any event, simply waste power.

2) An E.Q. Amplifier 131 which provides a slight equalization curve toensure that the acoustic output is flat down to 20 Hz, a necessaryfeature because the intrinsic frequency response of the subwoofer 50 andits cabinet 51, taken together, deviates from ideal flatness.

3) A Video Contour circuit 132 having back panel adjustability viatoggle switch 65 (FIGS. 1 and 12B) between video contour and flatoperation.

4) A Phase Amplifier 134 again having back panel adjustability via knob64 (FIGS. 1 and 12B) which allows the relative phase of the compositeaudio signal 126 to be varied from 0° to 180°, thus allowing the user toblend the subwoofer 50 with the user's main loudspeakers which typicallyreplicate only the upper bass frequencies, mid-range frequencies, andtreble frequencies while the subwoofer 50 produces a very low frequencyoutput audio signal. By adjusting the Phase Amplifier 134, relativelyseamless acoustic response can be obtained in the overlap region wherethe subwoofer 50 acoustic output mixes with the acoustic output of themain speakers.

5) A Crossover Frequency circuit 135 having back panel adjustability viaknob 62 (FIGS. 1 and 12B) allowing the user to adjust the point at whichthe subwoofer 50 begins to play, enabling the subwoofer 50 to reproducefrequencies as high as 75 Hz or frequencies at 35 Hz and below with the55 Hz mid-point being normal. The setting of the Crossover Frequencycontrol circuit 135 depends on the frequency range of the main channelspeakers that the subwoofer 50 is to be used with.

6) A volume control 136 defined by variable resistor VR1 having backpanel adjustability via knob 61 (FIGS. 1 and 12B) enabling the user toadjust the volume of the audio signal output from the subwoofer 50.

7) A Line Amplifier 138 which serves to amplify the composite audiosignal 126.

8) An Opto-Coupler 139 which optically couples the composite audiosignal 126 to the downstream signal processing stages. Optical couplingis highly desirable because it helps to eliminate “ground loops” andattendant hum—i.e., extraneous noise—caused by “ground loops”.

9) An Overshoot Control circuit 141 which serves to clamp any transientsignals that occur to a factory predetermined maximum level

10) A Clipping Eliminator circuit 146 which serves to limit the drivesignal to an absolute maximum level.

The Clipping Eliminator circuit 146 and Overshoot Control circuit 141comprise the upstream circuits included within the Master ProtectionCircuit 140 (FIGS. 12A and 12B) to be described in greater detail below.The Clipping Eliminator circuit 146 and Overshoot Control circuit 141each receive the composite audio input signal 126 from the Opto-Coupler139, with the Clipping Eliminator 146 providing an output control signalthat is input to the Overshoot Control circuit 131 and serves to controlthat circuit.

In order to prevent the subwoofer 50 from being overdriven atfrequencies below 25 Hz, the composite audio signal output from theovershoot Control circuit 141 is input, in parallel, to: i) an ExcursionLimiter circuit 142 (FIG. 25); and ii), a Low Frequency Auto Throttlecircuit 143 (FIG. 26). The Excursion Limiter circuit 142 serves to limitthose very low frequencies that might damage or overload the subwoofer50 in the manner described below; while the Low Frequency Auto Throttlecircuit 143 comprises the sensing and control circuits which areemployed to activate or control the normally inactive Excursion Limitercircuit 142, again in a manner to be described below.

In carrying out this objective of the invention, and as best observed byreference to FIG. 25, it will be noted that the Excursion Limitercircuit 142 essentially comprises a high pass filter which has,nominally, a corner frequency of 18 Hz—i.e., the low limit response ofthe subwoofer 50. That is, in normal operation, the Excursion Limitercircuit 142 serves to attenuate signals below 18 Hz, preventing themfrom passing through the signal processing circuitry while, at the sametime, allowing all signals above 18 Hz to pass through undiminished.However, under certain circumstances, it is desirable to prevent fullamplitude signals below 25 Hz from passing through the signal processingsystem—viz., when the subwoofer 50 is driven to its maximum allowablemechanical limits, yet normal output is desired.

To accomplish this, the composite audio signal 126 output from theOvershoot Control circuit 141 is applied simultaneously to both theExcursion Limiter circuit 142 (FIG. 25) and the Low Frequency AutoThrottle circuit 143 (FIG. 26). As will be noted upon reference to FIGS.12B, 25 and 26 conjointly, the composite audio signal 126 output fromthe Overshoot Control circuit 141 is applied to input terminal T1 forboth the Excursion Limiter circuit 142 (FIG. 25) and the Low FrequencyAuto Throttle circuit 143 (FIG. 26). Within the Excursion Limitercircuit 142 (FIG. 25), the composite audio signal 126 is fed viaresistor R7 and capacitors C5, C6 and C7 to the positive input port ofan operational amplifier OP3. Resistors R7, R8 and R9, together withcapacitors C5, C6 and C7, constitute a frequency determining networkthat combines with operational amplifier OP3 to form the high passfiltering function. Diodes D7, D8 are provided to prevent theoperational amplifier OP3 from exceeding its common mode range, thuscausing distortion. The thus filtered composite audio signal 126 outputfrom the operational amplifier OP3 is output at terminal T3 to aClipping Level circuit 144 described below in connection with FIG. 26;and, additionally, is fed back to the negative input port of operationalamplifier OP3.

Under those conditions where the woofer 50 is being driven to itsmaximum allowable mechanical limits and, nonetheless, more output isrequired, the Low Frequency Auto Throttle control line which is coupledto input terminal T2 of the Excursion Limiter 142 (FIG. 25) is pulleddownwardly towards ground by the action of the Low Frequency AutoThrottle control circuit 143 (FIG. 26), thus inserting an additionalresistor in parallel with resistor R10 (FIG. 25) in the ExcursionLimiter circuit 142, effectively changing the value of resistor R10 and,therefore, changing the corner frequency from 18 Hz to 25 Hz. Thisserves to attenuate frequencies below 25 Hz and reduces the audioresponse by 4 dB compared to the level before the effective resistanceof resistor R10 (FIG. 25) was reduced. To accomplish this, the compositeaudio signal at input terminal T1 is simultaneously applied to both theExcursion Limiter circuit 142 (FIG. 25) and to the Low Frequency AutoThrottle circuit 143 (FIG. 26). In the Low Frequency Auto Throttlecircuit 143 (FIG. 26), the composite audio signal 126 is fed to diodesD9, D10 via resistor R11 and capacitor C8 which together form an RC timeconstant and attenuate the high frequency components of the audio signalso that: i) low frequency components of the audio signal 126 arrive atdiodes D9, D10 at full amplitude; while ii), high frequency componentsof the audio signal 126 are reduced in amplitude. The positive portionsof the audio signal 126 are passed through diode D9 to the negative portof an operational amplifier OP4, while the negative portions of theaudio signal are passed through diode D10 to the positive port of theoperational amplifier OP4. Resistors R12 and R14 (R14 forms a feedbacknetwork around operational amplifier OP4), control the gain of theamplifier OP4, while resistor R13 comprises a ground return resistor fordiode D10. The ground return resistor for diode D9 is resistor R12 sincethe negative input port of the operational amplifier OP4 is,essentially, a virtual ground.

The output of operational amplifier OP4 comprises a negative-goingsignal 127 which is passed through diode D11 to charge up capacitor C9.Resistor R15 comprises a current limiting resistor which serves toprotect operational amplifier OP5. Resistor R16 is provided to form adischarge path for the voltage on capacitor C9 resulting from thenegative output signal 127 from operational amplifier OP4. The magnitudeof the negative voltage on capacitor C9 is dependent on the amplitude ofthe audio input signal 126 as rectified by diodes D9, D10; and,consequently, as the negative voltage level on capacitor C9 becomeslarger—i.e., more negative—than a predetermined threshold established byresistors R17, R18, operational amplifier OP5 flips HIGH, passing apositive voltage level through a current limiting resistor R20 andturning transistor Q3 ON. When transistor Q3 is turned ON, resistor R21is pulled to ground, effectively placing resistor R22 (FIG. 26) inparallel with resistor R10 (FIG. 25). Resistor R19 comprises ahysteresis resistor which serves to prevent instability of operationalamplifier OP5 when the latter is operating very close to its thresholdlevel. In short, the signal at the output of transistor Q3 is eitherHIGH (positive) as indicated at 133 a or LOW (negative) as indicated at133 b; and, the position at which it transitions is determined byresistors R17, R18. When the signal 133 b output from transistor Q3 isLOW (negative), the Low Frequency Auto Throttle circuit 143 is turnedOFF; and, when the signal 133 a output from transistor Q3 is HIGH(positive), the Low Frequency Auto Throttle circuit 143 is turned ON,momentarily throttling the low frequencies in the audio signal 126 beingpassed through the Excursion Limiter circuit 142 (FIG. 25) by impressingthe HIGH signal level 128 on the audio signal 126 being fed to thepositive input port of operational amplifier OP3 (FIG. 25) via terminalT2—the output terminal from the Low Frequency Auto Throttle circuit 143of FIG. 26 and one of the two (2) input terminals for the ExcursionLimiter circuit 142 of FIG. 25.

Thus, those skilled in the art will appreciate that when the LowFrequency Auto Throttle circuit 143 determines that dangerously lowfrequencies are overstressing the subwoofer 50, the Low Frequency AutoThrottle circuit 143 is turned ON, throttling the undesirable lowfrequency signals. When the dangerously low frequency signals disappear,the Low Frequency Auto Throttle circuit 143 trips back to its OFF state.

In carrying out the present invention, the composite audio signal 126output from the Excursion Limiter 142 (FIG. 25) on terminal T3 is inputto the positive input port of an Throttle Set circuit 148 is coupled toa Thermal Integrator circuit 149 where it is attenuated slightly byresistor R27, rectified by diode D12 to form a negative voltage that isproportional to the average voltage value at junction 151, and input tothe negative input port of an operational amplifier OP7. Resistors R27,R28 and capacitor C11, together with diode D12, form an averagingcircuit which produces an input signal to the negative input port ofoperational amplifier OP7 that is, on average, roughly proportional tothe temperature of the voice coil 104 (FIGS. 3 and 4) since resistor R28and capacitor C11 define an electrical time constant that is roughlyequivalent to the thermal time constant of the mass of the woofer 54 andits voice coil 104. Resistor R29 sets the hysteresis level foroperational amplifier OP7. Consequently, when the woofer 54 begins tooverheat, the magnitude of the voltage level on capacitor C11 becomestoo large, exceeding the threshold of operational amplifier OP7 set byresistors R30, R31. This causes an output signal from the operationalamplifier OP7 in the Thermal Integrator 149 which is HIGH, indicatingthat the subwoofer 54 is too hot. The HIGH signal level output fromoperational amplifier OP7 is fed via resistor R32, a buffer resistor fortransistor Q4, to the base of transistor Q4, turning the transistor ON.

When transistor Q4 is turned ON, it inserts resistor R33 in parallelwith resistor R26 in the Manual Throttle Set circuit 148, reducing theoutput voltage at the junction 151 by 3 dB. Consequently, the drivesignal to the subwoofer 54 is, in terms of power, reduced to half of itsformer value, allowing the subwoofer 54 to begin to cool down. When thesubwoofer 54 has cooled sufficiently, the operational amplifier OP7 inthe Thermal Integrator 139 flips from HIGH to LOW as the capacitor C11is being discharged.

The composite audio signal 126 impressed on junction 151 is then fed tothe input of an Impulse Damper circuit 145 whose function and operationis described in detail below. However, before discussing the ImpulseDamper circuit 135 in detail, it may be helpful to an understanding ofthis facet of the present invention to briefly describe the operationand relationship of the mass driven driver 52 (FIGS. 2 and 5)—i.e., the“passive radiator”—and the voice coil driven driver 54. In the case ofthe voice coil driven driver 54, it will be understood from theforegoing description, particularly in the light of the ensuingdescription relating to FIGS. 28 through 32, that the movable drivecomponents of the voice coil driven driver 54—viz., the voice coilformer 102, voice coil 104, speaker cone 100, dust cover 105, decorativecover 106, surround 78′ and spider 108, all of which are resilientlysupported from the basket-like frame or cage 90 of the subwoofer 54—arereciprocated axially through a peak-to-peak stroke of about 2.5″ byalternately delivering (+)−v and (−)−v signals to the voice coil 104from the Driver Amplifier 190. The mass driven subwoofer 52, or “passiveradiator”, on the other hand, moves outwardly and inwardly through aPUSH/PULL peak-to-peak stroke of up to about 2.5″ in reaction tomovement of the voice coil driven woofer 54 and consequent changes inair pressure within the cabinet 51 (FIGS. 1 and 2).

“Passive radiators” are well known to persons skilled in the art; and,it will be understood that the mass driven subwoofer 52 or “passiveradiator” employed with the present invention does not, of and byitself, constitute an inventive feature of the invention. Nevertheless,its structure and operation do contribute to the lightness in weight ofthe subwoofer 50 of the present invention and to the ability of thesubwoofer to function at high efficiency in a very small cabinet 51.More specifically, and as is well known to persons skilled in the art,assume that operation of the subwoofer 50 is initiated when the movablecomponents of both the mass driven subwoofer 52 and the voice coildriven subwoofer 54 are initially at rest, and in the null or neutralposition shown in solid lines in FIG. 5. Assume further that the DriverAmplifier 190 (FIG. 3) initially delivers a (+)−v voltage signal to thevoice coil 104 in the voice coil driven subwoofer 54.

Under these assumed operating conditions, it will be understood that themovable components of the voice coil driven subwoofer 54 will begin tomove outwardly in a PUSH stroke of up to about 1.25″ from the null orneutral position. As the voice coil driven subwoofer's movablecomponents begin to move outwardly, the air contained within the sealedcabinet 51 (FIG. 2) begins to rarefy, causing the mass 85 forming partof the mass driven subwoofer 52 to start moving inwardly in a PULLstroke of up to about 1.25″. Of course, it will be understood thatmovement of the mass driven woofer 52 lags behind movement of thepositively driven voice coil driven woofer 54. When the driver amplifier190 then delivers a (−)−v signal 104 to the voice coil driven subwoofer54, the latter begins to move inwardly in a PULL stroke towards andthrough the null or neutral position and through a peak-to-peak strokeof up to about 2.5″ from the dotted line position shown in FIG. 5towards the dashed line position, thus beginning to compress the airwithin the sealed cabinet 51. As the voice coil driven subwoofer 54begins to initiate its inward or PULL stroke, the mass driven subwoofer52 is still completing its inward or PULL stroke where its movement isgoverned by the following:

F=Ma=(Mdv/dt)  [7]

where “M” equals the mass of the subwoofer's movable components, “a”equals acceleration, “dv” equals incremental changes in velocity, and“dt” equals incremental changes in time.

Movement of the voice coil driven subwoofer 54 is, of course, governedby the following:

F=il×{right arrow over (B)}=Bli  [8]

where “i” equals the current in to voice coil 104, “l” equals the lengthof the voice coil 104, and “{right arrow over (B)}” equals the magneticfield.

During approximately the first half cycle of operation, the movablecomponents of the voice coil driven subwoofer 54 and the mass drivensubwoofer 52—i.e., the “passive radiator”—are out of synchronism withmovement of the mass driven subwoofer 52 lagging behind that of thevoice coil driven subwoofer 54. However, following the initialapproximate half cycle of operation, the mass driven subwoofer 52catches up with the voice coil driven subwoofer 54 and the movablecomponents of the two subwoofers 52, 54 begin to move in synchronismwith both moving outwardly simultaneously in a PUSH stroke of up toabout 1.25″ and both moving inwardly simultaneously in a PULL stroke ofup to about 1.25″—i.e., a peak-to-peak stroke of up to about 2.5″.

During the initial approximate half cycle of operation when the massdriven subwoofer 52 is still moving inwardly while the voice coil drivensubwoofer 54 is moving outwardly, air pressure within the cabinet 51 isinsufficient to prevent the voice coil driven subwoofer 54 from beingoverdriven; and, during this brief period of time, the voice coil drivensubwoofer 54 can be damaged unless steps are taken to control the motionof the movable components in the voice coil driven subwoofer 54.

To resolve this problem, the composite audio signal 126 output fromjunction 151 in the Manual Throttle Set circuit 148 (FIG. 27) is routedto the positive input port of an operational amplifier OP8 forming partof an Impulse Damper circuit 145. Assuming an initial start-up conditionof silence—i.e., the movable components of both the mass drivensubwoofer 52 and the voice coil driven subwoofer 54 are at rest and inthe null or neutral solid line position shown in FIG. 5—then thetransistor Q5 in the Impulse Damper circuit 145 is turned OFF. Whentransistor Q5 is OFF, the resistors R37, R38 form a voltage dividerwhich reduces the level of the composite audio signal 126 output onterminal 154 to the Woofer Servo 155 (FIG. 28). Assuming, however, thata sudden and explosive transient audio signal is presented to thepositive input port of the operational amplifier OP8 in the ImpulseDamper circuit 145—for example, a loud drum beat—the signal output fromthe operational amplifier OP8 is rectified by a diode D13 and passedthrough resistor R34 to charge up capacitor C12 (resistor R34 andcapacitor C12 form a time delay circuit). When capacitor C12 is fullycharged up, transistor Q5 is turned ON, the full gain of the system isrealized, and the composite audio output signal 126 at terminal 154 ismaximized. Capacitor C12 is discharged by resistor R35; and,consequently, when the explosive transient signal goes away, the ImpulseDamper circuit 145 automatically resets itself to a low gain state withtransistor Q5 OFF until the next explosive transient occurs. Thoseskilled in the art will appreciate that the Impulse Damper circuit 145is a proportional circuit—i.e., one in which the gain change is roughlyproportional to voice coil velocity. In the exemplary circuit here shownin FIG. 27, resistor R36 is the drive resistor for transistor Q5.

In order to ensure that the audio sounds emanating from the subwoofer 50of the present invention are as free of distortion as possible,provision is made for sensing whether the moving components of the voicecoil driven subwoofer 54 are moving in a linear non-distorted fashion orare moving in a non-linear distorted fashion; and, wherein distortednonlinear motions are sensed and generate a signal which isproportional, but inverted, with respect to the sensed non-lineardistorted motion of the subwoofer and are impressed on the undistortedcomposite audio signal 126 being processed. To accomplish this, thecomposite audio signal 126 output on terminal 154 of the Impulse Damper(FIG. 27) comprises a first input which is routed to the positive portof an operational amplifier OP9 in a Woofer Servo circuit 155 (FIGS. 13and 28) which is generally conventional in both circuit architecture andfunction. The second, or “sensed”, input to the Woofer Servo 155comprises a signal generated by accelerometer 109 (FIG. 3) which isfixed to the voice coil former 102 forming part of the voice coil drivensubwoofer 54. As is conventional with accelerometers 109 of the typehere depicted at 109 in FIG. 3, it senses whether the movement of themovable components of the voice coil driven subwoofer 54 are or are notnon-linear. The accelerometer 109 serves to output a signal on lines156, 158 which is proportional to the acceleration of the movingcomponents of the voice coil driven subwoofer 54.

Acceleration of the subwoofer 54 is, in turn, proportional to theamplitude of the motion; and, consequently, when the amplitude of themotion of the subwoofer 54 is non-linear, the output of theaccelerometer 109 is also non-linear. The Woofer Servo 155 serves tocompare the output signal from the accelerometer 109 with thenon-distorted composite audio input signal 126.

To accomplish this, the sensed output signal from the accelerometer109—which is a replica of the motion of the voice coil 104 and othermoving components of the voice coil driven subwoofer 54—is fed to anoperational amplifier OP10 (FIG. 28) in the Woofer Servo circuit 155.The input impedance to operational amplifier OP10 is established byresistors R39, R40 and capacitor C13, while resistor R41 sets the gainof the operational amplifier OP10. A variable resistor VR2 is providedso as to enable the operational amplifier OP10 to be adjusted to eachindividual driver during installation and thus ensure that propercircuit loop gain is provided.

The output signal from operational amplifier OP10—which is a replica ofthe undistorted composite audio signal 126 being input to the positiveinput port of operational amplifier OP9, but which has any senseddistorted components on it amplified by operational amplifier OP10, isfed, out-of-phase with the undistorted composite audio signal 126, tothe negative input port of operational amplifier OP9. Thus, operationalamplifier OP9 algebraically sums the undistorted composite audio signal126 presented at its positive input port and the distorted signal outputfrom the accelerometer 109 and presented at its negative input port.This serves to ensure that the composite audio signal 126 output fromthe operational amplifier OP9 on terminal 159 is a distorted audio drivesignal; but, the distortion is substantially equal and opposite to thedistortion resulting from the sensed non-linear movement of thesubwoofer 54. As a consequence, the distorted composite audio drivesignal 126 output from the operational amplifier OP9 on terminal 159serves to substantially cancel, to the extent possible, the distortionssensed by the accelerometer 109. Resistors R42, R43 serve to set thegain of operational amplifier OP9. Resistors R44, R45 and capacitor C14form the compensation poles and zeros to compensate the feedback systemas is conventional with Woofer Servo circuitry such as depicted at 155in FIG. 28.

The distorted composite audio drive signal 126 output from the WooferServo 155 on terminal 159 is then passed through the Buffer 160 (FIG.13) to the Diode Steering Network 165 (FIGS. 13 and 29) which serves to:i) pass the distorted composite audio drive signal 126, unaltered andundisturbed, directly to the Driver Amplifier 190 (FIGS. 13, 29 and 30)for a purpose to be described in greater detail below; and ii), to splitthe distorted composite audio drive signal 126 into its positiveportions (+)126 and its negative portions (−)126. To this end, the DiodeSteering Network 165 includes resistors R46, R47, R48, R49 and a pair ofdiodes D14, D15. Resistors R46, R47 serve to bias diode D14 on the diodethreshold—viz., 0.6 v—while resistors R48, R49 similarly bias diode D15.Stated differently, resistors R46 through R49 are selected such that a0.6 v positive voltage level appears at the junction 167 a betweenresistors R46, R47; and, a 0.6 v negative voltage level appears at thejunction 167 b between resistors R48, R49. This arrangement serves toensure that all of the audio information in the positive portions (+)126of the composite audio signal 126 is passed through diode D14 on line168, while all of the audio information in the negative portions (−)126of the composite audio signal 126 is passed through diode D15 on line169.

In order to better understand the operation of the Diode SteeringNetwork 165 depicted in FIG. 29, attention is now directed to FIG. 30.Thus, it will be observed that the distorted composite audio drivesignal 126 output from the Woofer Servo 155 and buffer 160 is input tothe midpoint 167 c of the resistor pairs R46, R47 and R48, R49. Both thepositive and negative portions of the distorted composite audio drivesignal 126 are fed via line 166 to the Driver Amplifier 190. ResistorsR46, R47 serve to ensure that only the positive portions (+)126 of thecomposite audio drive signal 126 are passed through diode D14 via line168 to the (+) Tracking Downconvertor Power supply 170, while resistorsR48, R49 serve to ensure that only the negative portions (−)126 of thecomposite audio drive signal are passed through diode D15 via line 169to the (−) Tracking Downconvertor Power Supply 180. In keeping with thepresent invention, the (+) and (−) Tracking Downconvertor Power Supplies170, 180 respectively serve to generate and output (+)−v and (−)−voutput signals in a manner described in further detail below inconnection with FIGS. 31A-31C; and, such (+)−v and (−)−v output signalsare input, to the Driver Amplifier 190.

In order to simplify an understanding of the ensuing description of thecircuit architecture and operation of the (+) and (−) TrackingDownconvertor Power Supplies 170, 180, attention is directed to FIGS.31A-31C—but, especially, FIG. 31B—where the circuitry for the (+)Tracking Downconvertor Power Supply 170 has been shown in detail andwill be described hereinbelow. The (−) Tracking Downconvertor PowerSupply 180 has been illustrated in FIG. 31C simply in block-and-lineform; and its operation will not be described in detail. However, thoseskilled in the art will appreciate that the operation of the (−)Tracking Downconvertor Power Supply 180 is identical to that of the (+)Tracking Downconvertor Power Supply 170 except for the fact that the (−)Tracking Downconvertor Power Supply 180 serves to operate on thenegative portions (−)126 of the composite audio signal 126 as outputfrom the Steering Diode Network 165 and as shown in FIG. 30 to produce(−)−v output signals, while the (+) Tracking Downconvertor Power Supply170 operates on the positive portions (+)126 of the composite audiosignal 126 to produce (+)−v output signals.

Referring now to FIGS. 31B and 31C, it will be observed that thepositive portions (+)126 of the distorted composite audio drive signal126 output on line 168 from the Steering Diode Network 165 (FIG. 30) areinput to the positive input port of an operational amplifier OP11forming a (+) Comparator 176 in the (+) Tracking Downconvertor PowerSupply 170. At the same time, the negative portions (−)126 of thedistorted composite audio drive signal 126 output on line 169 of theSteering Diode Network 165 are input to the (−) Comparator 186 (FIG.31C). The audio output from operational amplifier OP11 is routed to thepositive input port of an operational amplifier OP12 in a (+) Ramp TimeModulator 171 via resistor R51 which functions in conjunction withcapacitor C15 to form a high frequency filter network to prevent radiofrequency interference (RFI) from affecting the operation of thecircuit. The output of operational amplifier OP12 comprises a series ofpulses whose duty cycle is proportional to the amplitude of the positiveportions (+)126 of the distorted composite audio drive input signal 126.Thus, when the amplitude of the positive portions (+)126 of the audiosignal 126 are large, the duty cycle is high; and, when the amplitude ofthe positive portions (+)126 of the audio signal 126 is low, the dutycycle is small. The output from the operational amplifier OP12 is routedto a light emitting diode LED1 in an opto-coupler 177 and is coupledacross a space to a light sensitive trigger 178 forming part of theopto-coupler 177, thus causing a similar series of pulses to appear atthe output of the opto-coupler 177.

As best shown in FIG. 31A, and in keeping with the present invention,the (+) and (−) Tracking Downconvertor Power Supplies 170, 180 (FIGS.31B, 31C) each include a common Pulse Generator 200 and a common SquareWave-To-Triangular Wave Convertor 201. Pulse generator 200 includesresistors R52, R53, R54, R55 and R56, a pair of operational amplifiersOP13, OP14, and a timing capacitor C16 as the circuitry employed togenerate pulses. The value of capacitor C16 determines the speed atwhich pulses are generated—in this exemplary case, 130 Khz. The outputof the Pulse Generator comprises a series of steady state rectangularpulses 215 (FIG. 20) which are delivered to the (+) input port ofoperational amplifier OP15 forming part of the Square Wave-To-TriangularWave Convertor 201. Resistor R57 and capacitor C17, together withoperational amplifier OP15, serve to convert the steady staterectangular pulses 215 (FIG. 20) to triangular pulses 216 (FIG. 21).Capacitor C18 couples the triangular pulses 215 (FIG. 20) to thenegative input port of operational amplifier OP12 in the Ramp TimeModulator 171 (FIG. 31B) while resistors R58, R59 provide apositive-going voltage which forces the Ramp Time Modulator 171 tocontinue supplying pulses even in the absence of an audio signal 126 sothat the (+)−v and (−)−v signals output from the (+) and (−) TrackingDownconvertor Power Supplies 170, 180 (FIGS. 31B, 31C) never go to zero,but, rather, only to ±6 volts with the (+)−v and (−)−v signals rangingfrom ±6 volts to ±140 volts.

In the Ramp Time Modulator 171, resistor R60 comprises a pull-upresistor enabling power to flow into the the light sensative trigger 178in light emitting diode LED1, while resistor R61 is a pull-up resistorenabling power to flow into the optocoupler 177. Capacitors C19, C20 andC22, together with diode D16, are power suppression filter componentsfor the opto-coupler 177. A pull-up resistor R62 is provided to enablepower to flow into the bases of the transistors Q6, Q7 to turn thetransistors ON. Resistor R63 and capacitor C22 comprise components atthe output of the driver circuitry consisting of transistors Q6, Q7which serve to slightly slow down the drive pulses so as to avoidgenerating radio frequency interference (RFI). Capacitors C23, C24 areRFI suppression components.

The signal output from the Ramp Time Modulator 171 is input to the (+)Switch 172 via resistors R64, R65, R66, R67 which all comprisesuppression components. Resistor R68 comprises a safety resistor toensure that there is always a ground return path for the high impedancefield effect transistors FET1, FET2, FET3. A boot strap power supply isprovided by capacitor C25, resistor R69 and diode D17 when the fieldeffect transistors FET1, FET2, FET3 are OFF. At this time, the voltageat the output of the field effect transistors FET1, FET2, FET3 is LOW;and, when this occurs, the negative end of capacitor C23 is locked toground through diode D5 which is forward conducting during that periodof time, permitting current to flow from the 13 volt supply throughcapacitor C25, resistor R69 and diode D17 so as to charge up capacitorC23—i.e., the charge on capacitor C25 is transferred to capacitor C23through resistor R69 and diode D17. When capacitor C23 is fully chargedand fixed HIGH, the power supply for the circuit is from capacitor C23rather than capacitor C25, enabling current flow from capacitor C23 torun the circuitry for the Ramp Time Modulator 171. The outputs from thefield effect transistors FET1, FET2, FET3 are filtered by inductor L1and capacitor C3. The purpose of diode D5 is to supply continuousconduction when the field effect transistors FET1, FET2, FET3 are OFF.Capacitors C26, C27 comprise RF suppression components with capacitorsC26 and C27 being in parallel with the +160 volt main power supply,again serving to prevent RFI.

In operation, the (+)−v output signal from the Power Output Section 174of the (+) Tracking Downconvertor Power Supply 170—i.e., inductor L1,capacitor C3 and diode D5—are routed to: i) the Driver Amplifier 190 viaoutput terminal 220; and ii), the (+) Power Output Feedback Section 175which provides an input to the negative port of the (+) Comparator 176therein. Since the audio signal input to the positive input port of the(+) Comparator has a peak voltage of only 13 volts, while the (+)−vvoltage levels peak at 153 volts, the (+) Power Output Feedback Section184 includes resistors R70, R71, R72 which comprise a voltage divider todrop the peak 153 volt (+)−v signal to in the range of about a 13 voltpeak signal so that when the input signals are added together in the (+)Comparator 176, they are compatible in amplitude, value and size.

Turning now to FIG. 32 depicting the schematic circuitry for anexemplary Driver Amplifier 190 embodying features of the presentinvention, it will be noted that the distorted composite audio drivesignal 126 output from the Diode Steering Network 165 (FIGS. 29, 30) online 166, is routed as an enabling signal to input terminal 191 of theDriver Amplifier 190 and impressed upon the base of transistor Q8through resistor R73, an RFI suppression resistor. Transistors Q8 and Q9form a differential pair having a plus input port (the base oftransistor Q8) and a minus input (the base of transistor Q9) wherein theplus input port of transistor Q8 receives the audio input signal 126 andthe minus input port of transistor Q9 receives a feedback signal. Theoutput of transistor Q8 drives transistor Q10. The output of transistorQ10 then drives transistors Q11, Q12 which, in turn, drive the outputtransistors Q1, Q2 (FIGS. 14A, 14B and 32). Resistor R75 serves tosupply current to transistors Q8, Q9, while resistor R74 is a loadcollection resistor for transistor Q8. Resistor R77 is an emitterresistor for transistor Q10. Resistor R78 and diodes D18, D19, D20 serveto supply current to transistors Q10, Q11, Q12. The diodes D18, D19, D20form a barrier voltage (0.6 volts×3) of about 1.8 volts to bias uptransistors Q11 and Q12, thereby eliminating crossover distortion.Output transistors Q1, Q2 are power transistors which receive theirpower in the form of (+)−v and (−)−v signals from respective ones of the(+) and (−) Tracking Downconvertor Power Supplies 170, 180; and, theoutput of transistors Q1, Q2 provide input signals to: i) drive thevoice coil driven subwoofer 54 by alternately supplying (+)−v and (−)−vsignals to the voice coil 104; and ii), the feedback network fortransistor Q9 comprising resistors R79, R76. Capacitor C28, which iszero, compensates for the feedback loop.

In accordance with another of the important aspects of the presentinvention, and as best seen by reference to FIG. 33, provision is madefor completely eliminating the undesired “ground loops” and the voltagegenerated across the broken grounds, thereby completely eliminating theproblem of “ground loop” induced 60 Hz hum in a subwoofer. To accomplishthis, the composite audio signal 126 output from the Input Buffers 125(FIGS. 12A and 24) is routed to the negative input port of anoperational amplifier OP16 in the Ground Loop Hum Eliminator 124 viainput terminal 230 and resistor R80; and, at the same time, thecomposite audio signal 126 is also routed from input terminal 230directly to the positive input port of a second operational amplifierOP17. Operational amplifier OP16 comprises an inverting amplifier whichdrives opto-coupler 231; while operational amplifier OP17 is a unitygain buffer that drives a second opto-coupler 232. A first pair ofresistors R80, R81 serve to set the gain of operational amplifier OP16;a second pair of resistors R82, R83 set the gain of opto-coupler 231;and, a third pair of resistors R84, R85 set the gain of opto-coupler232.

As a consequence, the composite audio signal 126 input to operationalamplifier OP16 is inverted at the output 234 of operational amplifierOP16, appearing as an inverted audio signal (126), and is then fed to alight emitting diode LED2 in the opto-coupler 231, generating lightwhich is detected by a light sensitive transistor Q13 in theopto-coupler 231. The output signal generated by transistor Q13 is thenfed to the negative input port of a second inverting operationalamplifier OP18. A capacitor C29 serves to couple the A.C. components ofthe inverted audio signal (126) at the junction 235 between thetransistor Q13 and the resistor R83 to operational amplifier OP18 whichserves to again invert the previously inverted composite audio signal(126), producing a non-inverted composite audio signal 126 at its output236. Resistor R86 sets the gain of operational amplifier OP18.

At the same time, the original non-inverted composite audio signal 126input to the Ground Loop Hum Eliminator 124 at terminal 230 is routed tothe positive input port of operational amplifier OP17 which comprises aunity gain buffer, reproducing the composite audio signal 126 innoninverted form at its output 238. That audio signal 126 is then routedto light emitting diode LED3 in optocoupler 232, generating a lightsignal conveyed to a light sensitive transistor Q14. The output oftransistor Q14 is conveyed to the positive input port of operationalamplifier OP19, a unity gain Buffer, through capacitor C30 which servesto couple the A.C. components of the signal 126 at the junction 239between the transistor Q14 and resistor R85 to the operational amplifierOP19. The non-inverted composite audio signal 126 at the output 240 ofoperational amplifier OP19 is then combined with the non-invertedcomposite audio signal 126 at the output 236 of operational amplifierOP18 by resistors R87, R88, with the audio signal appearing at thejunction 241 of resistors R87, R88 being routed to the output terminal242 of the Ground Loop Hum Eliminator 124 as a non-inverted compositeaudio signal 126 to be then fed to the Subsonic Filter 130 as shown atFIG. 12A.

In the event that an undesired, unwanted “ground loop” induced 60 Hz humvoltage or signal 243 should appear across the input grounds 244 andoutput grounds 245, the opto-couplers 231, 232 will route the hum signal243 to respective ones of the operational amplifier OP18, an invertingamplifier, and OP19, a unity gain amplifier. Since the non-inverted humsignals 243 at the inputs to the two operational amplifiers OP18, OP19are in phase, the inverted hum signal (243) at the output 236 ofinverting operational amplifier OP18 will be out of phase—i.e.,inverted—with respect to the hum signal 243 at the output 240 ofoperational amplifier OP19. Consequently, when the inverted hum signal(243) at the output 236 of operational amplifier OP18 is combined withthe non-inverted hum signal 243 at the output 240 of operationalamplifier OP19 by resistors R87, R88, the two hum signals (243), 243cancel to zero.

Thus it will be seen that the input grounds 244 and output grounds 245are separated or isolated by the opto-couplers 231, 232, thereby“breaking” the grounds and preventing closed “ground loops”. Any humvoltage 243 generated across the broken grounds 244, 245, will becancelled due to the phase inversion action of operational amplifierOP18 and summing resistors R87, R88. Finally, the composite audio signal126 is not cancelled because the audio signal 126 is inverted (out ofphase) by operational amplifier OP16, and then inverted a secondtime—i.e., reinverted—by operational amplifier OP18, so that thecomposite audio signal 126 at the output 236 of operational amplifierOP18 is in phase with the composite audio signal 126 at the output 240of operational amplifier OP19; and, when these two in phase compositeaudio signals 126 are combined by resistors R87, R88, a composite audiosignal 126 devoid of 60 Hz hum induced by “ground loops” is produced atthe junction 241 of resistors R87, R88 and is output to the SubsonicFilter 130 (FIG. 12A) via output terminal 242.

In accordance with another of the important features of the presentinvention, provision is made for maintaining the tinsel leads 112 (FIGS.3, 34A, 34B and 34C) under tension during all portions of thepeak-to-peak 2.5″ excursion of the movable components of the voice coildriven woofer 54 during PUSH/PULL operation thereof. Thus, as best shownin FIG. 34A where the speaker cone 100 and voice coil former 102 areshown in their neutral or null positions, the tinsel lead 112 extendsoutwardly over a resilient piece of compressible/expandable polyethylenefoam 225 which is attached to the basket-like frame or cage 90 of thevoice coil driven woofer with the outboard end of the tinsel lead beingattached to the frame 90 as shown in FIG. 3. When the movable componentsof the voice coil driven woofer move outwardly during a PUSH stroke fromthe position shown in FIG. 34A to that shown in FIG. 34B, the resilientpolyethylene foam element 225 expands and serves to maintain the tinselleads 112 under tension, thereby preventing them from flapping againstthe speaker cone as the latter moves. Similarly, when the movablecomponents of the voice coil driven woofer 54 move inwardly during aPULL stroke from the null position shown in FIG. 34A to the positionshown in FIG. 34C, the tinsel lead 112 serves to compress thepolyethylene foam element 225 which again maintains the tinsel leadsunder tension and prevents them from flapping against the speaker cone100 and causing undesired noise.

Those skilled in the art will appreciate from the foregoing descriptionthat the subwoofer 50 of the present invention, although totallycontained in a sealed cabinet 51 only 11″×11″×11″ defining an internalvolume of space of only about 0.4 ft³ to about 0.5 ft³—as contrastedwith conventional prior art subwoofers typically requiring cabinetsenclosing a volume of space ranging from about 8 ft³ to about 27 ft³—is,nevertheless, characterized by its ability to output as much bass outputas the extremely large conventional prior art subwoofers. This ispossible for the following principle reasons:

Those skilled in the art will appreciate from the foregoing descriptionthat the subwoofer 50 of the present invention, although totallycontained in a sealed cabinet 51 only 11″×11″×11″ defining an internalvolume of space of only about 0.4 ft³ to about 0.5 ft³—as contrastedwith conventional prior art subwoofers typically requiring cabinetsenclosing a volume of space ranging from about 8 ft³ to about 27 ft³—is,nevertheless, characterized by its ability to output as much bass outputas the extremely large conventional prior art subwoofers. This ispossible for the following principle reasons:

1. The subwoofer 50 of the present invention is characterized by havingdrivers 52, 54 capable of moving in and out of the very small woofercabinet 51 through peak-to-peak strokes of up to about 2.5″—i.e.,maximum a peak-to-peak stroke that is from five to six times greaterthan that achievable with conventional prior art subwooferconfigurations.

2. The subwoofer 50 of the present invention includes a mass drivenwoofer 52 and a voice coil driven woofer 54 in which the movable drivercomponents are supported solely by a flexible surround 78, 78′ and aflexible spider 89, 108. The surrounds 78, 78′ are uniquelycharacterized by their construction and rigidity, each having athickness ranging from about 0.1″ to about 0.14″, or more, and anedgeroll having a diameter of about 1.5″ as contrasted with conventionalprior art surrounds having thicknesses on the order of 0.02″ andedgerolls having diameters less than 1″. The surrounds 78, 78′ of thepresent invention are capable of withstanding internal box pressureswhich are an order of magnitude greater than the internal box pressuresgenerated in conventional prior art subwoofers while retaining themovable driver components stable and substantially free of wobble asthey move through their peak-to-peak stroke of up to about 2.5″.

3. Since the subwoofer 50 of the present invention is contained totallywithin a very small sealed cabinet defining an internal volume of spaceranging from about 0.4 ft³ to about 0.5 ft³—i.e., a cabinet ranging fromabout {fraction (1/15)}th to about {fraction (1/67)}th the size of acabinet employed in conventional prior art subwoofers—as the movablecomponents of the mass driven subwoofer 52 and the voice coil drivensubwoofer 54 move in and out of the cabinet 51, a very high air pressureis generated within the cabinet 51—viz., up to about 3 lbs/in² and, inthe exemplary form of the invention from about 1.5 lbs/in² to about 3lbs/in²; or, a pressure sufficient to impose a force of 150 lbs. on atypical 8″ diameter speaker cone 100 (FIG. 3). Therefore, in order toovercome the high air pressure generated within the cabinet 51, atracking downconvertor drive amplifier—viz., the (+) and (−) TrackingDownconvertor Power Supplies 170, 180 and Driver Amplifier 190—isrequired which is capable of: i) delivering on the order of 2,700 wattsrms into a nominal 4 ohm resistive load; ii) swinging 104 volts rms; andiii) delivering only about 150 to 200 watts (300 to 400 watts on a timelimited basis) maximum power to the voice coil 104, preventingoverheating and enabling generation of large quantities of power withhigh efficiency.

4. The weight of the magnet 94 employed with the present invention isapproximately 225 oz. (i.e., approximately 14 lbs, 1 oz.)—that is, themagnet 94 employed with the present invention is approximately 5½ to 11times larger than the magnets commonly employed in prior art subwooferswhere the magnet typically weighs not more than 20 ounces, and, at most,40 ounces—and, consequently, the back emf generated within the subwooferof the present invention is extremely high, allowing the driver 54 to beoperated far away from the stall mode and, consequently, at anefficiency more than ten times greater than a conventional subwoofer ofcomparable size could possibly achieve.

It will, it is believed, facilitate an understanding of the presentinvention if a brief description is set forth at this point as to atypical subwoofer's operation relative to the stall mode and theefficiencies achieved resulting from generating a large backemf—something achievable only with subwoofers 50 embodying features ofthe present invention.

Virtually all, if not all, conventional prior art subwoofers areoperated very close to stall—an operating mode characterized by verylittle output power and large amounts of current flowing through thecoils of the motor—viz., the voice coil and the magnet—thus making themotor run very hot. In the present invention, however, the electricmotor of the subwoofer—i.e., the voice coil 104 and magnet 94—isoperated far away from the stall mode. This serves to generate a largeback emf. That is, most voltage delivered to the voice coil 104 is, ineffect, cancelled by the back emf generated within the motor (voice coil104/magnet 94) by virtue of the driver's approximate 2.5″ peak-to-peakexcursion.

More particularly, because the voice coil 104 is moving inwardly andoutwardly with a relatively long peak-to-peak excursion of up to about2.5″, the voice coil 104 cuts many lines of magnetic flux in themagnetic structure. As those skilled in the art will appreciate, it isthe rate of flux change that generates back emf, and, consequently, thelarge peak-to-peak stroke or excursion of the voice coil 104 within themagnet structure not only moves large amounts of air but, moreimportantly, it serves to generate a large back emf. In conventionalprior art subwoofers, the voice coil typically moves through apeak-to-peak stroke of only about 0.4″ to only about 0.6″—viz., thepeak-to-peak stroke of the driver of the present invention is from aboutfive to about six times greater than the maximum peak-to-peak strokesachieved with a conventional prior art subwoofer configuration—within amagnetic field generated by a very small magnet (a magnet typicallyweighing only about 20 oz.); and, consequently, conventional prior artsubwoofers are incapable of generating a large back emf. This results intoo much current flow in the voice coil winding, causing the subwooferto overheat; and, therefore, requires large, heavy and expensive heatdissipation systems.

A further requirement for generating a large back emf is the provisionof a very high magnetic flux field—again a requirement that cannot bemet with conventional prior art subwoofers which typically employmagnets weighing not more than 20 ounces; occasionally employing magnetsweighing up to 28 ounces; and, in rare cases employing magnets weighingas much as 40 ounces. The magnet 94 employed with the present invention,however, weighs approximately 225 ounces or, it is an order of magnitudelarger than magnets typically employed with conventional prior artsubwoofers. Consequently, as the voice coil 104 moves within the veryhigh magnetic flux field produced by the extremely large magnet 94through a peak-to-peak stroke of up to about 2.5″, a large back emf isgenerated due to the large stroke of the voice coil 104 cutting manylines of force. This is, of course, not possible with conventionalsubwoofers where: i) the voice coil typically moves with a peak-to-peakstroke on only about 0.4″ to about 0.6″; ii) the magnet weighs onlyabout 20 oz.; and iii), therefore, the magnetic flux field is small andrelatively few lines of force are cut.

Thus having in mind the foregoing discussion and recognizing that: i)the voice coil 104 and magnet 94 of the present invention are operatedfar from the stall mode, thus generating a large back emf; ii) that theinvention contemplates the use of a very large annular magnet having anO.D. of approximately 7{fraction (11/16)}″, an I.D. of approximately3.5″, and a weight of approximately 225 ounces, and is, therefore,capable of generating a very high magnetic flux field B; iii) theinvention employs a pole piece 98 having a diameter of approximately 3″;iv) the voice coil 104 is a four-layer winding having an overall woundlength of approximately 2″ and reciprocates in a magnetic gap 99 of upto about 0.25″; v) the voice coil 104 is reciprocating throughpeak-to-peak strokes ranging up to about 2.5″ and, therefore, cuts manylines of flux; and vi), the subwoofer 50 of the present invention iscapable of operating at frequencies f as low as 20 Hz, it is relativelyeasy and well within the ability of persons skilled in the art, tocompute comparative back emf levels for the present invention on the onehand and conventional prior art subwoofers on the other hand.

Thus, the back emf generated in a typical 8″ Dia. voice coil drivensubwoofer, or driver 54, made in accordance with the present invention,operating at a frequency f of, for example, 25 Hz, and employing amagnet 94, pole piece 98, and voice coil 104 having the foregoingdimensional and/or weight characteristics, is established by:

back emf=dφ/dt  [4]

where:

dφ/dt=Blv=Bl Aω cos ωt  [9]

where: i) B is the magnetic flux field generated by the exemplarymagnet/pole piece combination 94/98 of the present invention; ii) l isthe length of the voice coil 104 in the magnetic gap 99; and iii), v isequal to velocity, where the velocity v is, in turn, equal to A ω cos ωtand A is equal to the maximum peak stroke of the voice coil 104 (i.e.,one-half of the peak-to-peak excursion), ω is equal to 2πf where f isassumed equal to 25 Hz, and cos ωt is equal to 1 corresponding to thepeak velocity. Consequently, in order to calculate back emf generatedwith the present invention assuming: (i) a frequency f of 25 Hz; andii), a peak-to-peak stroke of 2.5″ for the voice coil 104—viz., amaximum peak stroke of 1.25″ (or 0.03175 meters)—or a peak-to-peakstroke of 2.0″ defining a peak stroke of 0.1″ (or 0.0254 meters), oneskilled in the art must first compute the values of B (flux) and l (thelength of the voice coil 104 wire within the magnetic gap 99).

To compute the value of flux B, one skilled in the art will recognizethat the following well-known equation yields B:

B≅(A ₁ /A ₂)B _(r)  [10]

where A₁ is the radial or transverse surface area of the magnet 94, A₂is the radial or transverse surface area of the pole piece 98, and B_(r)is retentivity (a value capable of being determined by reference tocommonly available “look up” tables). Since the O.D. and I.D. of theannular magnet 94 and the diameter of the pole piece 98 are all knownquantities, substituting in equation [10] and simplifying produces:

B≅[(7{fraction (11/16)})²−(3.5)²]/3² ×B _(r)  [10]

or, B≅(59−12.2)/9×B_(r) and, therefore:

B≅5.194(B _(r)).  [10]

However, B_(r) (retentivity) is a known quantity. See, e.g., REFERENCEDATA FOR ENGINEERS, Seventh Edition, chapter entitled “Saturation FluxDensitys,” where the value of B_(r) for a magnet such as the exemplarymagnet 94 ranges from 0.16 to 0.24 and averages 0.20.

Therefore:

B≅5.194(0.20)≅1.0388 Teslas.  [10]

In order to compute the approximate length l of that portion of thevoice coil 104 in the magnetic gap 99, one skilled in the art needs todetermine: i) the axial length of the magnetic gap 99 between the gapplate (top plate 92) and the voice coil 104; and ii), the length l ofthe wire forming that portion of the voice coil 104 in the magnetic gap99. The axial length of the magnetic gap 99 defined by the gap plate(top plate 92) is, by definition (as well known to persons skilled inthe art), one-quarter of the diameter of the pole piece 98—viz., ¼×3″equals 0.75″. In other words, those skilled in the art will recognizethat the flux density in the pole piece 98 and the flux density in thegap plate (top plate 92) must be made equal for optimum magnetic design.This means that their respective areas must be the same—i.e., A₂ equalsA₃ where A₂ is the radial or transverse area of the pole piece 98 and A₃is the inner circumferential area of the annular gap plate (top plate92).

As to the overall length of the wire in the voice coil 104, it is knownfrom the foregoing description that the voice coil 104 is a four-layerwinding of approximately 2″ overall length; and, persons skilled in theart will know that such windings are typically formed of copper wire.Solving a simple arithmetic problem wherein the thickness of themagnetic gap (0.25″) is known, as is the overall length (2″) of thevoice coil winding 104 and the fact that the winding is a four-layerwinding, shows that the wire gauge must be 23 in order for the voicecoil winding 104 to fit inside the specified gap, allowing the voicecoil winding 104 to reciprocate in a magnetic gap 99 of up to about0.25″ in radial width without impinging upon or rubbing against the gapplate (top plate 92) or other fixed structural components of the driver54.

Thus, one can readily determine that the overall length of the wiredefining the voice coil 104 is approximately 195 feet, or approximately59 meters; and, since only 0.375″ of the overall 2″ length of the woundvoice coil 104 is in the gap 99 at any given point in time, then thelength l of the voice coil 104 in the magnetic gap 99 at any given timeis 0.375″ (59) or, about 22.1 meters. Therefore, Bl≅B(1.0388Teslas)×1(22.1 meters)≅22.9 Tesla-meters. However, those skilled in theart will appreciate that no magnetic geometry is perfect and,consequently, some lines of force will be lost. To compensate for thisfact, Bl will be assumed to approximate only 19.5 Tesla-meters—viz.,only about 85 percent of the theoretical value computed above.

Accordingly, substituting in equation [9]:

Back emf=Bl(A)(2πf) (cos ωt);  [9]

and, therefore:

Back emf=19.5(0.03175)(2π25)(1)=97.25 volts peak or 68.6 volts rms(97.25×0.707)  [9]

where the long excursion stroke equals 2.5″ or 0.03175 meters peak.

Alternatively, where the long excursion stroke equals 2″ and the maximumpeak stroke is, therefore, 0.0254 meters, substituting in equation [9]produces:

Back emf=19.5(0.0254)(2π25)(1)=77.8 volts peak or 55 volts rms.  [9]

Obviously, as the frequency f increases from the assumed frequency of 25Hz to, for example, 40 Hz, 60 Hz, 80 Hz, etc., the back emf willincrease proportionally assuming that the peak-to-peak stroke remains at2.5″. However, in normal operation, and as a practical matter, as thefrequency f increases, the peak-to-peak stroke will generally decreasefrom the maximum peak-to-peak stroke of about 2.5″; and consequently,while the back emf generated by the present invention may increasesomewhat above 97.25 volts peak (or 77.8 volts rms) as computed above,it will not, in normal operation, increase to several hundred volts peakeven where the frequency f rises to, for example, 100 Hz.

If the frequency f in the foregoing example is increased from 25 Hz to30 Hz, and assuming the maximum peak stroke A remains at 0.03175 meters,then:

Back emf=19.5(0.03175)(2π30)(1)=116.7 volts peak or 82.51 voltsrms.  [9]

The significant back emf generated by the present invention becomesquite remarkable when compared to the back emf generated by a normal orstandard sized prior art 8″ Dia. driver using a relatively small magnetweighing, for example, 25 ounces, having a peak-to-peak stroke of 0.6″defining a maximum peak stroke of 0.00762 meters, and operating at afrequency f of 25 Hz. Thus, it is known that with such relatively smalllight-weight magnetic structures, the value of Bl will typically rangefrom about 5 Tesla-meters to about 8 Tesla-meters. Therefore, assumingan above average Bl value of 7 Tesla-meters for such a conventionaldriver, and substituting in equation [9], it will be determined:

Back emf=7(0.00762)(2π25)(1)=8.38 volts peak or 5.92 volts rms  [9]

where the peak-to-peak stroke equals a maximum of 0.6″ and, therefore,the maximum peak stroke is 0.00762 meters.

Where the frequency f of such a conventional prior art subwoofer isincreased from 25 Hz to 30 Hz, then:

Back emf=7(0.00762)(2π30)(1)=10.05 volts peak or 7.10 volts rms.  [9]

Indeed, even assuming there exists a prior art 8″ Dia. subwoofer with amagnetic structure sufficiently large to generate a Bl volume of 11Tesla-meters—a highly unlikely possibility—then:

Back emf=11(0.00762)(2π25)(1)=13.16 volts peak or 9.31 volts rms  [9]

In short, the back emf generated by a conventional 8″ diameter prior artsubwoofer having a relatively small light-weight magnetic structure willbe only about 9.5 percent of the back emf generated by the voice coildriven driver 54 of the present invention assuming, of course, that bothare being operated at the same frequency. Not even the worst case upperlimit of the back emf of a conventional 8″ subwoofer falls within theback emf range of an 8″ subwoofer constructed in accordance with thisinvention. In that regard, assuming a situation in which a conventional8″ subwoofer is driven to the point at which the voice coil “bottomsout” (typically about 0.8″ peak-to-peak), and assuming magneticstructure generating a Bl of 11 Tesla-meters results in a back emf of17.6 volts peak (approximately 12.5 volts rms) at a frequency of 25Hertz. In comparison, substituting values discussed herein that apply toan 8″ subwoofer constructed in accordance with the invention results ina range of back emf values substantially in excess of 13 volts rms up toabout 100 volts rms at a frequency of 25 Hertz.

However, the large back emf generated with the use of a longpeak-to-peak stroke of the voice coil 104 within a very high magneticflux field provided by a large magnet weighing approximately 225 ounces,produces a further problem conventional prior art subwoofers are unableto cope with. That problem is related to the fact that when the back emfis very high, as it is with the present invention, the applied emf tothe woofer must be even greater than the back emf in order to overcomeit.

In the present invention, this problem is solved by employing anextremely powerful amplifier—viz., a tracking downconvertor driveamplifier (170, 180, 190) capable of delivering 2,700 watts rms into anominal 4 ohm resistive load, and which can swing 104 volts rms.However, despite employment of such an extremely powerful amplifier, thewoofer 50 of the present invention does not overheat and/or burn upwhile the moving driver components are moving in and out through the2.5″ peak-to-peak stroke because the presence of a large back emfprevents the flow of damaging stall mode currents in the voice coil 104that would normally flow in the subwoofer 50 if it were a simpleresistive load. Rather, only a small fraction of that current flows inthe voice coil 104; but, since the magnet 94 is so large and because thedrive force is equal to the magnetic field times the current—See,equation [8], supra—the force on the voice coil 104 to drive thesubwoofer 54 and move the air is immense even though very little currentis flowing in the voice coil 104. However, where, as here, the magnet 94is extremely large (i.e., approximately 225 ounces), the back emfgenerated reduces the volts available, and this leads to the need for aspecial tracking downconvertor drive amplifier 170, 180, 190.

In the present invention, where the subwoofer 50 operates far from thestall mode, the tracking downconvertor drive amplifier defined by the(+) and (−) Tracking Downconverter Power Supplies 170, 180 and theDriver Amplifier 190 operates at approximately 88% efficiency. Thismeans that at an input of 200 watts, 176 watts are delivered to thevoice coil 104. Indeed, at full output power, the subwoofer 50 of thepresent invention requires delivery of only 360 watts (for an acousticoutput of 115 dB) to the voice coil 104.

In summary, the subwoofer 50 of the present invention is characterizedby: i) being flat to 18 Hz; ii) each driver 52, 54 can move 125 in³ ofair; iii) extremely low distortion; iv) a built-in trackingdownconvertor drive amplifier (170, 180, 190) capable of delivering2,700 watts rms into a nominal 4 ohm resistive load and swinging 104volts rms; and v), generation of a large back emf attributable to theuse of an extremely large magnet (225 ounces) and a voice coil 104moving through a peak-to-peak stroke of up to about 2.5″ in a very smallcabinet 51 (approximately 11″×11″×11″) defining an enclosed volume ofspace ranging from only about 0.4 ft³ to only about 0.5 ft³, all ofwhich cooperate to allow the subwoofer 50 to be operated far from thestall mode, whereas typical and conventional prior art subwoofers aredeliberately designed to operate close to the stall mode wherein largeamounts of current flow through the voice coil, generating a largeamount of heat that must be dissipated.

Another important feature characteristic of the present invention is theuse of a flexible suspension system for the movable driver componentsincluding solely a spider 89, 108 and a surround 78, 78′ wherein thesurround 78, 78′ ranges from about 0.1″ to 0.14″, or more, in thickness,employs an edgeroll 180 on the order of about 1.5″ in diameter, and iscapable of standing off the large internal box pressures—viz., up toabout 3 lbs/in² and, in the exemplary form of the invention, from about1.5 lbs/in² to about 3 lbs/in²—generated within the cabinet whilepermitting the movable driver components to move axially inward andoutward through a peak-to-peak stroke of up to about 2.5″ in a stablemanner and without significant wobble.

A further important feature characteristic of the present invention isthe provision of Input Buffers 125 (FIGS. 12A and 24) which serve to sumthe left and right channel audio input signals 120 a, 120 b at differentdB levels, thereby retaining both the L+R and L−R components of theaudio signal in a composite audio signal 126. Since the L−R component ofthe audio signal representing the stereo sound field is retained, thelife, luster, depth and impact of the audio sound is substantiallyenhanced for the listener.

Still another important feature characteristic of the present inventionis the provision of a Ground Loop Hum Eliminator 124 (FIGS. 12A and 33)which serves to completely eliminate both undesired “ground loops” andthe voltage generated across broken grounds, thereby completelyeliminating the problem of “ground loop” induced 60 Hz hum which, untilthe present invention, has continued to plague designers of conventionalprior art subwoofers.

Appendices

The Inventor is appending hereto Appendices “A” and “B” more fullyidentified below. Such Appendices comprise schematic circuit drawingsdepicting in greater detail the circuitry employed with the presentinvention, including component identification and values. It is intendedthat such appendices be made a part of the file history relating to thisapplication and, therefore, documents which are available for publicinspection by interested parties. It is not intended that theseAppendices be printed as part of any patent issuing from thisapplication.

It will be understood by persons skilled in the art that appendices “A”and “B” contain materials which are deemed sensitive and highlyproprietary by Applicant and his corporation—viz., SunfireCorporation—and are not to be duplicated, in whole or in part, withoutthe express written consent of Sunfire Corporation.

Appendix “A” comprises a size “D”, computer-generated schematic circuitdrawing—viz., Drawing No. 653-010-00 dated Jan. 22, 1996, with revisionsas of Mar. 26, 1997, entitled “True Subwoofer Amplifier”—here depictingcircuit details, including component identifications and values whereapplicable, of the (+) and (−) Tracking Downconvertor Power Supplies170, 180, Driver Amplifier 190 and Auto ON/OFF circuit employed with thepresent invention.

Appendix “B” comprises a size “D”, computer-generated schematic circuitdrawing—viz., Drawing No. 653-011-00, dated Jan. 22, 1996, withrevisions as of Mar. 19, 1997, entitled “Sunfire Subwoofer Preamp &Signal Processor”—here depicting circuit details, including componentidentifications and values where applicable for: i) an exemplary SignalProcessing Circuit including: Input Summing Buffers 125; a SubsonicFilter 130; an E.Q. Amplifier 131; a Zero to −180° Phase Amp 134; a THX®Amp; a Crossover Frequency circuit 135; a Bass Level Control 136;Voltage Regulators; a Line Amplifier 138; an Input Opto-Coupler 139;and, a Low-Pass Filter; ii) an exemplary Master Protection Circuit 140including: an Overshoot Control 141; a Clipping Eliminator 146; anExcursion Limiter 142; a Clipping Level circuit 144; a Low FrequencyAuto Throttle 143; a Thermal Integrator 149; and, a Thermal Protection(Trip circuit) 150; and iii), an Input Woofer Servo 155.

What is claimed is:
 1. A woofer apparatus for processing an audio signaland comprising: a) a cabinet having a chamber of a predetermined airvolume and at least one opening formed in the cabinet; b) a magnet whichis mounted to said apparatus and which establishes a magnetic field of apredetermined flux density; c) a voice coil member positioned toreciprocate in said magnetic field through maximum peak-to-peakexcursion strokes, and having a voice coil adapted to be operativelyconnected to a power amplifier; d) a speaker diaphragm mounted at saidopening and connected to said voice coil member for reciprocating motiontherewith through said maximum peak-to-peak excursion strokes; e)suspension for supporting said speaker diaphragm and said voice coilmember from said cabinet for reciprocation relative to said magnet; f)said apparatus being structured and configured so that as said speakerdiaphragm and said voice coil member reciprocate through maximumpeak-to-peak excursion strokes, the maximum pressure in said cabinet isgreater than 0.2 lbs/in² and back-emf generated in said voice coilmember is greater than 13 volts rms.
 2. The apparatus as recited inclaim 1, wherein said maximum peak-to-peak excursion strokes are greaterthan 0.6 inch.
 3. The apparatus as recited in claim 1, wherein saidmaximum peak-to-peak excursion strokes are substantially greater than0.6 inch.
 4. The apparatus as recited in claim 1, wherein said back-emfis substantially greater than 13 rms volts.
 5. The apparatus as recitedin claim 4, wherein said maximum peak-to-peak excursion strokes aregreater than 0.6 inch.
 6. The apparatus as recited in claim 4, whereinsaid maximum peak-to-peak excursion strokes are substantially greaterthan 0.6 inch.
 7. A woofer apparatus for processing an audio signal andcomprising: a) a cabinet having a chamber of a predetermined air volumeand at least one opening formed in the cabinet; b) a magnet which ismounted to said apparatus and which establishes a magnetic field of apredetermined flux density; c) a voice coil member positioned toreciprocate in said magnetic field through maximum peak-to-peakexcursion strokes and having a voice coil adapted to be operativelyconnected to a power amplifier; d) a speaker diaphragm connected to saidvoice coil member for reciprocating motion therewith through saidmaximum peak-to-peak excursion strokes; e) suspension for supportingsaid speaker diaphragm and said voice coil member from said cabinet forreciprocation relative to said magnet; f) said apparatus beingstructured and configured so the combination of the maximum peak-to-peakexcursions of the speaker diaphragm and the voice coil member, theeffective area of the diaphragm, the magnitude of the flux density ofthe magnetic field, the air volume of the cabinet, maximum acousticdisplacement of the apparatus, the effective length of the voice coil inthe peak current therein, is such that the maximum cabinet pressure issubstantially greater than 0.2 psi.
 8. The apparatus as recited in claim7, wherein said apparatus generates a back-emf in the voice coil withthe coil members reciprocating through maximum peak-to-peak excursionstrokes, said back-emf being greater than 13 volts rms.
 9. The apparatusas recited in claim 8, wherein said maximum peak-to-peak excursionstrokes are greater than 0.6 inch.
 10. The apparatus as recited in claim9, wherein said maximum peak-to-peak excursion strokes are substantiallygreater than 0.6 inch.
 11. The apparatus as recited in claim 8, whereinsaid back-emf at maximum peak-to-peak excursion strokes is substantiallygreater than 13 volts rms.
 12. The apparatus as recited in claim 11,wherein said maximum peak-to-peak excursion strokes are greater than 0.6inch.
 13. The apparatus as recited in claim 11, wherein said maximumpeak-to-peak excursion strokes are substantially greater than 0.6 inch.14. A woofer apparatus for processing an audio signal and comprising: a)a cabinet having a chamber of a predetermined air volume and at leastone opening formed in the cabinet; b) a magnet which is mounted to saidapparatus and which establishes a magnetic field of a predetermined fluxdensity; c) a voice coil member positioned to reciprocate in saidmagnetic field through maximum peak-to-peak excursion strokes and havinga voice coil adapted to be operatively connected to a power amplifier;d) a speaker diaphragm connected to said voice coil member forreciprocating motion therewith through said maximum peak-to-peakexcursion strokes; e) suspension for supporting said speaker diaphragmand said voice coil member from said cabinet for reciprocation relativeto said magnet; f) said apparatus being structured and configured sothat as said speaker diaphragm and said voice coil member reciprocatethrough maximum peak-to-peak excursion strokes, the combination of theeffective area (A) of the diaphragm and the flux density (B) of themagnetic field, relative to the air volume of the cabinet and maximumacoustic displacement of the apparatus and also relative to theeffective length () of the voice coil and peak current therein, so thatmaximum cabinet pressure is greater than 0.2 psi.
 15. The apparatus asrecited in claim 13, wherein said apparatus generates a back-emf in thevoice coil member so that as the voice coil member is reciprocatingthrough maximum peak-to-peak excursion strokes, said back-emf beinggreater than 13 volts rms.
 16. The apparatus as recited in claim 15,wherein said maximum peak-to-peak excursion strokes are greater than 0.6inch.
 17. The apparatus as recited in claim 16, wherein said maximumpeak-to-peak excursion strokes are substantially greater than 0.6 inch.18. The apparatus as recited in claim 15, wherein said back-emf atmaximum peak-to-peak excursion strokes is substantially greater than 13volts rms.
 19. The apparatus as recited in claim 18, wherein saidmaximum peak-to-peak excursion strokes are greater than 0.6 inch. 20.The apparatus as recited in claim 19, wherein said maximum peak-to-peakexcursions are substantially greater than 0.6 inch.
 21. A wooferapparatus for processing an audio signal and comprising: a) a cabinethaving a chamber of a predetermined air volume and at least one openingformed in the cabinet; b) a magnet which is mounted to said apparatusand which establishes a magnetic field of a predetermined flux density;c) a voice coil member positioned to reciprocate in said magnetic fieldthrough maximum peak-to-peak excursion strokes; and having a voice coiladapted to be operatively connected to a power amplifier; d) a speakerdiaphragm mounted at said opening and connected to said voice coilmember for reciprocating motion therewith through said maximumpeak-to-peak excursion strokes; e) suspension for supporting saidspeaker diaphragm and said voice coil member from said cabinet forreciprocation relative to said magnet; f) said apparatus beingstructured and configured so that as said speaker diaphragm and saidvoice coil member reciprocate through maximum peak-to-peak excursionstrokes, the maximum pressure in said cabinet is substantially greaterthan 0.2 lbs/in² and back-emf generated in said voice coil member isgreater than thirteen volts.
 22. The apparatus as recited in claim 21,wherein said maximum peak-to-peak excursion strokes are greater than 0.6inch.
 23. The apparatus as recited in claim 22, wherein said maximumpeak-to-peak excursion strokes are substantially greater than 0.6 inch.24. The apparatus as recited in claim 21, wherein said back-emf issubstantially greater than 13 rms volts.
 25. The apparatus as recited inclaim 24, wherein said maximum peak-to-peak excursion strokes aregreater than 0.6 inch.
 26. The apparatus as recited in claim 25, whereinsaid maximum peak-to-peak excursion strokes are substantially greaterthan 0.6 inch.
 27. A woofer apparatus for processing an audio signal,said apparatus comprising: a) a cabinet having a chamber of apredetermined air volume; b) a magnet which is mounted to said apparatusand which establishes a magnetic field of a predetermined flux density;c) a voice coil member positioned to reciprocate in said magnetic fieldthrough peak-to-peak excursion strokes during a maximum acousticdisplacement operating mode of the apparatus and having a voice coiladapted to be connected to an amplifier; d) a speaker diaphragmconnected to said voice coil member for reciprocating motion therewiththrough said peak-to-peak excursion strokes; e) suspension forsupporting said speaker diaphragm and said voice coil member from saidcabinet for reciprocation relative to said magnet; f) a passive radiatordiaphragm positioned to reciprocate through peak-to-peak excursionstrokes during said maximum acoustic displacement operating mode; g)said apparatus being structured and configured so that as said speakerdiaphragm with voice coil member and the passive radiator diaphragmreciprocate during maximum cabinet pressure mode of operation, theeffective area of said passive radiator diaphragm times its peak-to-peakexcursion stroke during said maximum acoustic displacement operatingmode plus the effective area of said speaker diaphragm times itspeak-to-peak excursion stroke during said maximum acoustic displacementoperating mode, relative to the flux density (B) of the magnetic field,the air volume of the cabinet, the effective length () of the voice coiland peak current therein, are such that the maximum box pressure issubstantially greater than 0.2 psi.
 28. A woofer apparatus forprocessing an audio signal and comprising: a) a cabinet having a chamberof predetermined air volume; b) a magnet which is mounted in saidapparatus and establishes a magnetic field of a predetermined fluxdensity; and which comprises a voice coil adapted to be operativelyconnected to a power amplifier; c) a voice coil member positioned toreciprocate in said magnetic field through maximum peak-to-peakexcursion strokes, and having a voice coil adapted to be connected to anamplifier; d) a speaker diaphragm connected to said voice coil memberfor reciprocating motion therewith through said maximum peak-to-peakexcursion strokes; e) a flexible resilient suspension for supportingsaid speaker diaphragm and said voice coil member from said frame forreciprocation relative to said magnet; f) said apparatus beingstructured so that as said speaker diaphragm and said voice coil memberreciprocate at 25 Hertz through a peak-to-peak stroke of 0.6 inches, thecombination of the effective flux density, the effective length () ofthe voice coil and peak current therein, are such so that the back-emfis substantially greater than 13 volts.
 29. A woofer apparatus forprocessing an audio signal and comprising, in combination: a) a cabinethaving a chamber of a predetermined air volume; b) a magnet which ismounted in said apparatus and which establishes a magnetic field of apredetermined flux density; c) a voice coil member positioned toreciprocate at a maximum acoustic displacement mode during operation insaid magnetic field through maximum peak-to-peak excursion strokes andhaving a voice coil adapted to be operatively connected to a poweramplifier; d) a speaker diaphragm mounted at said opening and connectedto said voice coil member for reciprocating motion therewith throughsaid maximum peak-to-peak excursion strokes; e) said apparatus beingstructured and configured so that as said speaker diaphragm and saidvoice coil member reciprocate during maximum acoustic displacementthrough said maximum peak-to-peak excursion strokes: i. the flux densityis sufficiently high relative to the effective length of the coil andrelative to peak operating current; and ii. the flux density issufficiently high and length of the peak-to-peak excursion stroke issufficiently great relative to the effective length of the coil, so thatsufficient force and power are developed to drive the diaphragm throughsaid maximum peak-to-peak excursion strokes and create peak cabinetpressure greater than 0.2 psi, whereby high acoustic displacement can beachieved relative to the air volume of the cabinet.
 30. A wooferapparatus for processing an audio signal and comprising: a) a cabinethaving a chamber of a predetermined air volume and at least first andsecond openings formed in the cabinet; b) a magnet which is mounted insaid apparatus and which establishes a magnetic field of a predeterminedflux density; c) a voice coil member positioned to reciprocate in saidmagnetic field through peak-to-peak excursion strokes at a maximumacoustic displacement operating mode and having a voice coil adapted tobe operatively connected to a power amplifier; d) a speaker diaphragmmounted in said first opening and connected to said voice coil memberfor reciprocating motion therewith through said peak-to-peak excursionstrokes during said maximum acoustic displacement operating mode; e) apassive radiator diaphragm positioned in said second opening toreciprocate through peak-to-peak excursion strokes during said maximumacoustic displacement operating mode; f) said apparatus being structuredand configured so that as said speaker diaphragm and said voice coilmember reciprocate during said maximum acoustic displacement operatingmode, the combination of the effective areas of said passive radiatordiaphragm and said speaker diaphragm, and the flux density (B) of themagnetic field, relative to the air volume of the cabinet and alsorelative to the effective length () of the voice coil and peak currenttherein, are such so that the maximum box pressure is substantiallygreater than 0.2 psi.
 31. A woofer apparatus for processing an audiosignal and being capable of producing a high acoustic displacementrelative to cabinet volume, said apparatus comprising: a) a cabinethaving a chamber of a predetermined air volume and at least first andsecond openings formed in the cabinet; b) an active driver sectioncomprising: i. a magnet which is mounted in said apparatus and whichestablishes a magnetic field of a predetermined flux density; ii. avoice coil member positioned to reciprocate in said magnetic fieldthrough peak-to-peak excursion strokes and having a voice coil which hasan effective coil length and is adapted to be operatively connected to apower amplifier; iii. an active speaker diaphragm which has an effectivediaphragm area and is connected to said voice coil member forreciprocating motion therewith through said excursion strokes to providean active acoustic displacement component; c) a passive radiator sectioncomprising a passive diaphragm which has an effective diaphragm area andis mounted in said second opening to travel through peak-to-peakexcursion strokes to provide a passive acoustic displacement component;d) said apparatus having a maximum total acoustic displacement operatingmode during which the active speaker diaphragm travels through itsactive peak-to-peak maximum acoustic displacement mode excursion strokesand the passive diaphragm travels through its passive peak-to-peakmaximum acoustic displacement mode excursion strokes; e) said apparatusbeing structured and configured so that as said active speaker diaphragmand said passive diaphragm reciprocate at maximum box pressure, thecombination of the effective area of said passive radiator diaphragm andthe effective area of said speaker diaphragm, the flux density of themagnetic field, relative to the air volume of the cabinet and alsorelative to the effective length () of the voice coil and peak currenttherein, is such, so that maximum box pressure is substantially greaterthan 0.2 psi.
 32. A woofer apparatus for processing an audio signalapparatus being capable of producing a high acoustic displacement whilehaving a relatively small cabinet volume, said apparatus comprising: a)a cabinet having a chamber of a predetermined air volume; b) an activedriver section comprising: i. a magnet which is mounted in saidapparatus and which establishes a magnetic field of a predetermined fluxdensity; ii. a voice coil member positioned to reciprocate in saidmagnetic field through peak-to-peak excursion strokes and having a voicecoil which has an effective coil length and is adapted to be operativelyconnected to a power amplifier; iii. an active speaker diaphragm whichhas an effective diaphragm area and is connected to said voice coilmember for reciprocating motion therewith through said excursion strokesto provide an active acoustic displacement component; c) a passiveradiator section comprising a passive diaphragm which has an effectivediaphragm area to travel through peak-to-peak excursion strokes toprovide a passive acoustic displacement component; d) said apparatushaving a maximum total acoustic displacement operating mode where thetotal of the active and the passive acoustic displacement components isat a maximum; e) said apparatus being structured and configured so thatas said active speaker diaphragm and the passive diaphragm reciprocatethrough their excursion strokes during the maximum total peakdisplacement operating mode, the combination of the effective areas (A)of the active speaker diaphragm and the passive diaphragm, and the fluxdensity (B) of the magnetic field , relative to the air volume of thecabinet and also relative to the effective length () of the voice coil,and peak current therein, so that the maximum box pressure is greaterthan 0.2 psi.
 33. A woofer apparatus for processing an audio signalapparatus and being capable of producing a high acoustic displacementrelative to cabinet volume, said apparatus comprising: a) a cabinethaving a chamber of a predetermined air volume and at least first andsecond openings formed in the cabinet; b) an active driver sectioncomprising: i. a magnet which is mounted in said apparatus and whichestablishes a magnetic field of a predetermined flux density; ii. avoice coil member which is positioned to reciprocate in said magneticfield through peak-to-peak excursion strokes in excess of 0.6 inches andwhich has an effective coil length and is adapted to be operativelyconnected to a power amplifier; iii. an active speaker diaphragm whichhas an effective diaphragm area and is connected to said voice coilmember for reciprocating motion therewith through said excursion strokesto provide an active acoustic displacement component; c) a passiveradiator section comprising a passive diaphragm which has an effectivediaphragm area and is mounted in said second opening to travel throughexcursion strokes to provide a passive acoustic displacement component;d) said apparatus having a maximum total acoustic displacement operatingmode during which the total of the active and passive acousticdisplacement components is at a maximum; e) said apparatus beingstructured and configured so that during the maximum total acousticdisplacement operating mode, the combination of the effective areas ofthe active speaker diaphragm and the passive diaphragm, and the fluxdensity of the magnetic field, relative to the air volume of thecabinet, and also relative to the effective length () of the voice coiland peak current therein, maximum box pressure is substantially greaterthan 0.2 psi.
 34. A woofer apparatus for processing an audio signalapparatus being capable of producing a high acoustic displacement whilehaving a relatively small cabinet volume, said apparatus comprising: a)a cabinet having a chamber of predetermined air volume; b) an activedriver section comprising: i. a magnet which is mounted in saidapparatus and which established a magnetic field of a predetermined fluxdensity; ii. a voice coil member which is positioned to reciprocate insaid magnetic field through maximum peak-to-peak excursion strokes inexcess of 0.6 inch and which has a voice coil which has an effectivecoil length and is adapted to be operatively connected to a poweramplifier; iii. an active speaker diaphragm which has an effectivediaphragm area and is connected to said voice coil member forreciprocating motion therewith through said excursion strokes to providean active displacement component; c) a passive radiator sectioncomprising a passive diaphragm which has an effective diaphragm area totravel through peak-to-peak excursion strokes to provide a passiveacoustic displacement component; d) said apparatus having a maximumtotal peak displacement operating mode during which the total of theactive and the passive acoustic displacement components is at a maximum;e) said apparatus being structured and configured so that as said activespeaker diaphragm and the passive diaphragm reciprocate through theirexcursion strokes during the maximum total acoustic displacementoperating mode, the combination of the effective areas of the activespeaker diaphragm and the passive diaphragm, the length of thepeak-to-peak excursion strokes of the voice coil member during themaximum acoustic displacement operating mode and the flux density (B) ofthe magnetic field are such, relative to the air volume of the cabinetand relative to the effective length () of the voice coil, and peakcurrent therein, so that the maximum box pressure is greater than 0.2psi.
 35. A woofer apparatus for processing an audio signal andcomprising: a) a cabinet having a chamber of a predetermined air volumeand at least one opening formed in the cabinet; b) a magnet which ismounted to said apparatus and which establishes a magnetic field of apredetermined flux density; c) a voice coil member positioned toreciprocate in said magnetic field through maximum peak-to-peakexcursion strokes at a maximum acoustic displacement operating mode, andhaving at least one voice coil adapted to be operatively connected to apower amplifier; d) a speaker diaphragm mounted at said opening andconnected to said voice coil member for reciprocating motion therewiththrough said maximum peak-to-peak excursion strokes; e) an amplifieroperatively connected to said voice coil to supply a signalrepresentative of an audio signal to the voice coil to drive the voicecoil member; f) suspension for supporting said speaker diaphragm andsaid voice coil member from said cabinet for reciprocation relative tosaid magnet; g) said magnetic field, said maximum peak-to-peak excursionstrokes of said voice coil during the maximum acoustic displacementoperating mode and the length of said at least one winding of said voicecoil collectively establishing a voice coil back-emf for limitingcurrent flow through said voice coil to a value that is substantiallyless than the rms voltage of the signal that is applied to said voicecoil to cause said current flow divided by nominal direct currentresistance of said voice coil; h) said apparatus being structured andconfigured so that as said speaker diaphragm and said voice coil memberreciprocate through peak-to-peak excursion strokes during a maximumacoustic displacement operating mode of the apparatus, the maximumpressure in said cabinet is greater than 0.2 lbs/in².
 36. A wooferapparatus as in claim 35 wherein the product of the magnetic field timesthe effective length of a winding of the voice during operation of saidapparatus is at least as great as about 20 Tesla-meters.
 37. A wooferapparatus as in claim 35 wherein the value of said magnetic field, saidpeak-to-peak excursion strokes of said voice coil at the maximumacoustic displacement operating mode, and the length of a winding ofsaid voice coil establish a voice coil back-emf that is substantially inexcess of 13 volts rms for an applied 25 Hertz sinusoidal signal of amagnitude sufficient to cause peak-to-peak excursion strokes of saidvoice coil member at the maximum displacement output operating mode. 38.A woofer apparatus for processing an audio signal and comprising: a) acabinet having a chamber of a predetermined air volume and at least oneopening formed in the cabinet; b) a magnet which is mounted to saidapparatus and which establishes a magnetic field of a predetermined fluxdensity; c) a movable driver component comprising: i. a voice coilmember positioned to reciprocate in said magnetic field throughpeak-to-peak excursion strokes at a maximum acoustic displacementoperating mode, and having a voice coil adapted to be operativelyconnected to a power amplifier; ii. a speaker diaphragm mounted at saidopening and connected to said voice coil member for reciprocating motiontherewith through said peak-to-peak excursion strokes; d) suspension forsupporting said speaker diaphragm and said voice coil member from saidcabinet for reciprocation relative to said magnet; said suspensioncomprising a surround formed of flexible, resilient, self-supportingmaterial, said surround having an edgeroll adjacent its outer periphery,with the outer boundary of said edgeroll being adapted for attachment ofsaid surround to a stationary portion of said apparatus, said surroundfurther having a region that is located inwardly of said edgeroll forattachment of said surround to the movable driver component, saidsurround being formed of a material and having a thickness that enablesoperation of said apparatus where maximum internal cabinet pressure isgreater than 0.2 lbs/in²; e) said apparatus being structured andconfigured so that as said speaker diaphragm and said voice coil memberreciprocate through peak-to-peak excursion strokes, during the maximumacoustic displacement operating mode, the maximum pressure in saidcabinet is greater than 0.2 lbs/in².
 39. The woofer apparatus of claim38, wherein said surround has a thickness that imparts rigidity andstrength to said surround that enables said surround to withstandmaximum internal box pressures within said cabinet that aresubstantially in excess of 0.2 lbs/in².
 40. A woofer apparatus as inclaim 38, wherein said surround has a thickness that is substantially inexcess of 0.02″.
 41. A woofer apparatus as in claim 38, wherein saidedgeroll of said surround has a diameter dimension in excess of 1.0″ andup to about 1.5″.
 42. A woofer apparatus as in claim 38, wherein saidsurround has a thickness that is between a value that is substantiallyin excess of 0.02″ and a value that is on the order of at least 0.14″and wherein said edgeroll of said surround has a diameter dimension inexcess of 1.0″ and up to about 1.5″.
 43. The apparatus of claim 42,wherein said surround of said suspension has a thickness in a range thatextends from about 0.1″ to at least 0.14″.
 44. The apparatus of claim38, wherein said surround of said resilient suspension system has athickness in a range that extends from about 0.1″ to at least 0.14″. 45.The apparatus of claim 38, wherein said surround is formed of nlaminations of surround foam having an initial aggregate thickness onthe order of at least 2{fraction (3/16)}″ compressed to a thickness onthe order of about 0.1″ or greater.
 46. The apparatus of claim 45,wherein said n laminations of surround foam are at least as great asfive laminations, each having an initial thickness on the order of about{fraction (7/16)}″ or greater.
 47. The apparatus of claim 45, whereinsaid n laminations of surround foam have an initial aggregate thicknesson the order of about 3{fraction (1/16)}″ or greater compressed to athickness on the order of about 0.1″ or greater.
 48. The apparatus ofclaim 45, wherein said n laminations of surround foam is at least asgreat as seven laminations, each having an initial thickness on theorder of about {fraction (7/16)}″ or greater.
 49. The apparatus of claim45, wherein said thickness of said surround and the diameter of saidedgeroll are selected to allow a maximum peak-to-peak excursion of thedriver components that exceed 0.6″.
 50. A woofer apparatus forprocessing an audio signal and comprising, in combination: a) a mountingframe; b) a magnet which is mounted to said frame and establishes amagnetic field of a predetermined flux density; c) a voice coil memberpositioned to reciprocate in said magnetic field through maximumpeak-to-peak excursion strokes, and comprising a voice coil adapted tobe operatively connected to a power amplifier; d) a speaker diaphragmconnected to said voice coil for reciprocating motion therewith throughsaid maximum peak-to-peak excursion strokes; e) a flexible resilientsuspension for supporting said speaker diaphragm and said voice coilmember from said frame for reciprocation relative to said magnet; f)said apparatus being structured so that as said speaker diaphragm andsaid voice coil member reciprocate through a maximum peak-to-peakexcursion stroke, the combination of the effective flux density, timessaid peak-to-peak stroke, relative to the effective length () of thevoice coil and peak current therein, is sufficiently high so that aback-emf of substantially greater than 13 volts is generated in saidvoice coil.
 51. The apparatus as recited in claim 50, wherein themaximum peak-to-peak excursion stroke is at least approximately 0.6inch.
 52. The woofer apparatus as recited in claim 50, wherein saidmounting frame comprises a plurality of mounting flanges by which themagnet is mounted to the frame.
 53. The woofer apparatus as recited inclaim 50, wherein said mounting frame has an annular frame portionpositioned radially outwardly of the speaker diaphragm, with saidflexible resilient suspension having an outer portion thereof connectedto said annular frame portion.
 54. The woofer apparatus as recited inclaim 53, wherein said surround has a configuration and thickness thatimparts rigidity and strength to said surround that enables saidsurround to withstand maximum pressure imposed on said speaker diaphragmand said surround in excess of 0.2 psi.
 55. A woofer apparatus forprocessing an audio signal and comprising: a) a cabinet having a chamberof a predetermined air volume and at least one opening formed in thecabinet; b) a magnet which is mounted to said apparatus and whichestablishes a magnetic field of a predetermined flux density; c) a voicecoil member positioned to reciprocate in said magnetic field throughpeak-to-peak excursion strokes at a maximum acoustic displacementoperating mode, and having at least one voice coil adapted to beoperatively connected to a power amplifier; d) a speaker diaphragmmounted at said opening and connected to said voice coil member forreciprocating motion therewith through said peak-to-peak excursionstrokes; e) an amplifier operatively connected to said voice coil tosupply a signal representative of an audio signal to the voice coil todrive the voice coil member; f) suspension for supporting said speakerdiaphragm and said voice coil member from said cabinet for reciprocationrelative to said magnet; g) said magnetic field, said peak-to-peakexcursion strokes of said voice coil during the maximum acousticdisplacement operating mode and the length of said at least one windingof said voice coil collectively establishing a voice coil back-emf forlimiting current flow thorough said voice coil to a value that issubstantially less than the rms voltage of the signal that is applied tosaid voice coil to cause said current flow divided by nominal directcurrent resistance of said voice coil; h) said apparatus beingstructured and configured so that as said speaker diaphragm and saidvoice coil member reciprocate through peak-to-peak excursion strokesduring a maximum acoustic displacement operating mode of the apparatus,the maximum pressure in said cabinet is greater than 0.2 lbs/in²,wherein the product of the magnetic field times the effective length ofa winding of the voice coil during operation of said apparatus is atleast as great as to about 20 Tesla-meters.
 56. A woofer apparatus forprocessing an audio signal and comprising: a) a cabinet having a chamberof a predetermined air volume and at least one opening formed in thecabinet; b) a magnet which is mounted to said apparatus and whichestablishes a magnetic field of a predetermined flux density; c) a voicecoil member positioned to reciprocate in said magnetic field throughpeak-to-peak excursion strokes at a maximum acoustic displacementoperating mode, and having at least one voice coil adapted to beoperatively connected to a power amplifier; d) a speaker diaphragmmounted at said opening and connected to said voice coil member forreciprocating motion therewith through said peak-to-peak excursionstrokes; e) an amplifier operatively connected to said voice coil tosupply a signal representative of an audio signal to the voice coil todrive the voice coil member; f) suspension for supporting said speakerdiaphragm and said voice coil member from said cabinet for reciprocationrelative to said magnet; g) said magnetic field, said peak-to-peakexcursion strokes of said voice coil member during the maximum acousticdisplacement operating mode and the length of said at least one windingof said voice coil collectively establishing a voice coil back-emf forlimiting current flow through said voice coil to a value that issubstantially less than the rms voltage of the signal that is applied tosaid voice coil to cause said current flow divided by nominal directcurrent resistance of said voice coil; h) said apparatus beingstructured and configured so that as said speaker diaphragm and saidvoice coil member reciprocate through peak-to-peak excursion strokesduring a maximum acoustic displacement operating mode of the apparatus,the maximum pressure in said cabinet is greater than 0.2 lbs/in².
 57. Asubwoofer apparatus for use in the home, said apparatus being capable ofproducing high acoustic displacement while having a relatively smallcabinet volume, said apparatus comprising: a) a cabinet having at leastone opening; b) a magnet disposed in said cabinet, said magnet producinga magnetic field having a flux density; c) a voice coil assembly adaptedto reciprocate in said magnetic field, said voice coil assemblyincluding a voice coil; d) a speaker diaphragm, having an effectivearea, driven from said voice coil assembly and mounted in said openingto reciprocate through peak-to-peak excursion strokes; e) a poweramplifier operatively connected to said voice coil and providing to saidvoice coil an electric current representative of an audio signal; and f)said apparatus being structured and configured so that the combinationof the maximum peak-to-peak excursion strokes, the effective area of thespeaker diaphragm, the flux density of the magnetic field, relative tothe cabinet air volume, the voice coil length, and peak current therein,is such so that the maximum cabinet pressure is greater than 0.2lbs./in².
 58. The apparatus as recited in claim 57, wherein said poweramplifier operates without a power transformer.
 59. The apparatus asrecited in claim 57, wherein said maximum peak-to-peak excursion strokesare substantially greater than 0.6 inches.
 60. The apparatus as recitedin claim 57, wherein, with said peak-to-peak excursion strokes of 0.6inches, said flux density, said voice coil length, and said peak-to-peakexcursion strokes establish a back-emf at least as great as 13 volts rmswhen a 25 Hz signal is supplied to said voice coil member.
 61. Theapparatus as recited in claim 57, wherein said apparatus comprises asurround connected to said diaphragm and having a thickness greater than0.02 inches.
 62. The apparatus as recited in claim 57, wherein saidapparatus comprises a surround connected to said diaphragm and havingthickness substantially greater than 0.02 inches.
 63. The apparatus asrecited in claim 57, wherein the volume enclosed by said cabinet is lessthan 1.0 ft.³.
 64. The apparatus as recited in claim 57, wherein saidpower amplifier is mounted in said cabinet.
 65. The apparatus as recitedin claim 57, wherein said apparatus comprises a surround formed of amaterial, and has a thickness, that enables operation of said subwooferapparatus with a maximum cabinet pressure in excess of 0.2 lbs/in². 66.The apparatus as recited in claim 57, said apparatus comprises asurround formed of a material, and has a thickness, that enablesoperation of said subwoofer apparatus with a maximum internal cabinetpressure substantially in excess of 0.2 lbs/in².
 67. A subwooferapparatus for use in the home, said apparatus being capable of producinghigh acoustic displacement while having a relatively small cabinetvolume, said apparatus comprising: a) a cabinet having at least oneopening; b) a surround disposed at said cabinet opening; c) a magnetdisposed in said cabinet, said magnet producing a magnetic field havinga flux density; d) a voice coil assembly adapted to reciprocate in saidmagnetic field, said voice coil assembly including a voice coil; e) aspeaker diaphragm having an effective area, driven from said voice coilassembly and mounted in said opening to reciprocate through peak-to-peakexcursion strokes; f) a power amplifier operatively connected to saidvoice coil and providing to said voice coil an electric currentrepresentative of an audio signal; g) said apparatus being structuredand configured so that the combination of the maximum peak-to-peakexcursion strokes, the effective area of the speaker diaphragm, the fluxdensity of the magnetic field, relative to the cabinet air volume, thevoice coil length, and peak current therein, is such so that the maximumcabinet pressure is greater than 0.2 lbs./in²; and h) said apparatusbeing structured and configured so that said surround comprises anedgeroll that has an outside diameter dimension greater than 1.0 inch.68. The apparatus as recited in claim 67, wherein, with saidpeak-to-peak excursion strokes of 0.6 inches, said flux density, saidvoice coil length, and said peak-to-peak excursion strokes establish aback-emf at least as great as 13 volts rms when a 25 Hz signal issupplied to said voice coil member.
 69. The apparatus as recited inclaim 67, wherein said power amplifier operates without a powertransformer.
 70. The apparatus as recited in claim 67, wherein saidmaximum peak-to-peak excursion strokes are greater than 0.6 inches. 71.The apparatus as recited in claim 67, wherein said maximum peak-to-peakexcursion strokes are substantially greater than 0.6 inches.
 72. Theapparatus as recited in claim 67, wherein said surround has a thicknessgreater than 0.02 inches.
 73. The apparatus as recited in claim 67,wherein said surround has a thickness substantially greater than 0.02inches.
 74. The apparatus as recited in claim 67, wherein said maximumpeak-to-peak excursion strokes, said voice coil length, and said fluxdensity establish a voice coil back-emf that is greater than 13 voltsrms when a 25 Hz signal is supplied to said voice coil assembly at anamplitude sufficient to cause said maximum peak-to-peak excursionstrokes.
 75. The apparatus as recited in claim 67, wherein said maximumpeak-to-peak excursion strokes, said voice coil length, and said fluxdensity establish a voice coil back-emf that is substantially greaterthan 13 volts rms when a 25 Hz signal is supplied to said voice coilmember at an amplitude sufficient to cause said maximum peak-to-peakexcursion strokes.
 76. The apparatus as recited in claim 67, wherein theenclosed volume of said cabinet is less than 1.0 ft.³.
 77. The apparatusas recited in claim 67, wherein said maximum cabinet pressure issubstantially greater than 0.2 lbs/in².
 78. The apparatus as recited inclaim 67, wherein said power amplifier is mounted in said cabinet. 79.The apparatus as recited in claim 67, wherein said surround is formed ofa material, and has a thickness, that enables operation of saidsubwoofer apparatus with a maximum cabinet pressure in excess of 0.2lbs/in².
 80. The apparatus as recited in claim 67, wherein said surroundis formed of a material, and has a thickness, that enables operation ofsaid subwoofer apparatus with a maximum internal cabinet pressuresubstantially in excess of 0.2 lbs/in².
 81. A subwoofer apparatus foruse in the home, said apparatus being capable of producing high acousticdisplacement while having a relatively small cabinet volume, saidapparatus comprising: a) a cabinet having at least one opening; b) amagnet disposed in said cabinet, said magnet producing a magnetic fieldhaving a flux density; c) a voice coil assembly adapted to reciprocatein said magnetic field, said voice coil assembly including a voice coil;d) a speaker diaphragm having an effective area, driven from said voicecoil assembly and mounted in said opening to reciprocate throughpeak-to-peak excursion strokes; e) a power amplifier operativelyconnected to said voice coil and providing to said voice coil anelectric current representative of an audio signal; f) said apparatusbeing structured and configured so that the combination of the maximumpeak-to-peak excursion strokes, the effective area of the speakerdiaphragm, the flux density of the magnetic field, relative to thecabinet air volume, the voice coil length, and peak current therein, issuch so that the maximum cabinet pressure is greater than 0.2 lbs./in²;and g) wherein said apparatus is structured and configured so that saidmaximum peak-to-peak excursion strokes, said voice coil length, and saidflux density establish a voice coil back-emf that is greater than 13volts rms when a 25 Hz signal is applied to said voice coil member at anamplitude sufficient to cause said maximum peak-to-peak excursionstrokes.
 82. The apparatus as recited in claim 81, wherein said poweramplifier operates without a power transformer.
 83. The apparatus asrecited in claim 81, wherein said apparatus comprises a surroundconnected to said diaphragm and having thickness greater than 0.02inches.
 84. The apparatus as recited in claim 81, wherein said apparatuscomprises a surround connected to said diaphragm and having thicknesssubstantially greater than 0.02 inches.
 85. The apparatus as recited inclaim 81, wherein the enclosed volume of said cabinet is less than 1.0ft.³.
 86. The apparatus as recited in claim 81, wherein said maximumpeak-to-peak excursion strokes are greater than 0.6 inches.
 87. Theapparatus as recited in claim 81, wherein said maximum peak-to-peakexcursion strokes are substantially greater than 0.6 inches.
 88. Theapparatus as recited in claim 81, wherein said maximum cabinet pressureis substantially greater than 0.2 lbs/in².
 89. The apparatus as recitedin claim 81, wherein said power amplifier is mounted in said cabinet.90. The apparatus as recited in claim 81, wherein said apparatuscomprises a surround formed of a material, and has a thickness, thatenables operation of said subwoofer apparatus with a maximum cabinetpressure in excess of 0.2 lbs/in².
 91. The apparatus as recited in claim81, wherein said apparatus comprises a surround formed of a material,and has a thickness, that enables operation of said subwoofer apparatuswith a maximum internal cabinet pressure substantially in excess of 0.2lbs/in².
 92. A subwoofer apparatus for use in the home, said apparatusbeing capable of producing high acoustic displacement while having arelatively small cabinet volume, said apparatus comprising: a) a cabinethaving at least one opening; b) a magnet disposed in said cabinet, saidmagnet producing a magnetic field having a flux density; c) a voice coilassembly adapted to reciprocate in said magnetic field, said voice coilassembly including a voice coil; d) a speaker diaphragm having aneffective area, driven from said voice coil assembly and mounted in saidopening to reciprocate through peak-to-peak excursion strokes; e) apower amplifier operatively connected to said voice coil and providingto said voice coil an electric current representative of an audiosignal; f) said apparatus being structured and configured so that thecombination of the maximum peak-to-peak excursion strokes, the effectivearea of the speaker diaphragm, the flux density of the magnetic field,relative to the cabinet air volume, the voice coil length, and peakcurrent therein, is such so that the maximum cabinet pressure is greaterthan 0.2 lbs./in²; and g) said maximum peak-to-peak excursion strokesbeing greater than 0.6 inches.
 93. The apparatus as recited in claim 92,wherein said power amplifier operates without a power transformer. 94.The apparatus as recited in claim 92, wherein said maximum peak-to-peakexcursion strokes are substantially greater than 0.6 inches.
 95. Theapparatus as recited in claim 92, wherein said voice coil back-emf issubstantially greater than 13 volts rms when a 25 Hz signal is suppliedto said voice coil member at an amplitude sufficient to cause saidmaximum peak-to-peak excursion strokes.
 96. The apparatus as recited inclaim 92, wherein, with said peak-to-peak excursion strokes of 0.6inches, said flux density, said voice coil length, and said peak-to-peakexcursion strokes establish a back-emf at least as great as 13 volts rmswhen a 25 Hz signal is supplied to said voice coil member.
 97. Theapparatus as recited in claim 92, wherein said apparatus comprises asurround connected to said diaphragm and having thickness greater than0.02 inches.
 98. The apparatus as recited in claim 92, wherein saidapparatus comprises a surround connected to said diaphragm and havingthickness substantially greater than 0.02 inches.
 99. The apparatus asrecited in claim 92, wherein the enclosed volume of said cabinet is lessthan 1.0 ft.³.
 100. The apparatus as recited in claim 92, wherein saidapparatus further comprises a power amplifier which is mounted in saidcabinet and connected to said voice coil member to supply a signalrepresentative of an audio signal to drive said voice coil member. 101.The apparatus as recited in claim 92, wherein said apparatus comprises asurround formed of a material, and has a thickness, that enablesoperation of said subwoofer apparatus with a maximum cabinet pressure inexcess of 0.2 lbs/in².
 102. The apparatus as recited in claim 92,wherein said apparatus comprises a surround formed of a material, andhas a thickness, that enables operation of said subwoofer apparatus witha maximum internal cabinet pressure substantially in excess of 0.2lbs/in².
 103. A subwoofer apparatus for use in the home, said apparatusbeing capable of producing high acoustic displacement while having arelatively small cabinet volume, said apparatus comprising: a) a cabinethaving at least one opening; b) a surround disposed at said cabinetopening; c) a magnet disposed in said cabinet, said magnet producing amagnetic field having a flux density; d) a voice coil assembly adaptedto reciprocate in said magnetic field, said voice coil assemblyincluding a voice coil; e) a speaker diaphragm having an effective area,driven from said voice coil assembly and mounted in said opening toreciprocate through peak-to-peak excursion strokes; f) a power amplifieroperatively connected to said voice coil and providing to said voicecoil an electric current representative of an audio signal; g) saidapparatus being structured and configured so that the combination of themaximum peak-to-peak excursion strokes, the effective area of thespeaker diaphragm, the flux density of the magnetic field, relative tothe cabinet air volume, the voice coil length, and peak current therein,is such so that the maximum cabinet pressure is substantially greaterthan 0.2 lbs./in²; and h) said apparatus being structured and configuredso that said surround comprises an edgeroll that has an outside diameterdimension greater than 1.0 inches.
 104. The apparatus as recited inclaim 103, wherein, with said peak-to-peak excursion strokes of 0.6inches, said flux density, said voice coil length, and said peak-to-peakexcursion strokes establish a back-emf at least as great as 13 volts rmswhen a 25 Hz signal is supplied to said voice coil member.
 105. Theapparatus as recited in claim 103, wherein said power amplifier operateswithout a power transformer.
 106. The apparatus as recited in claim 103,wherein said maximum peak-to-peak excursion strokes are greater than 0.6inches.
 107. The apparatus as recited in claim 103, wherein said maximumpeak-to-peak excursion strokes are substantially greater than 0.6inches.
 108. The apparatus as recited in claim 103, wherein saidsurround has a thickness greater than 0.02 inches.
 109. The apparatus asrecited in claim 103, wherein said surround has a thicknesssubstantially greater than 0.02 inches.
 110. The apparatus as recited inclaim 103, wherein said voice coil back-emf is greater than 13 volts rmswhen a 25 Hz signal is supplied to said voice coil member at anamplitude sufficient to cause said maximum peak-to-peak excursionstrokes.
 111. The apparatus as recited in claim 103, wherein said voicecoil back-emf is substantially greater than 13 volts rms when a 25 Hzsignal is supplied to said voice coil member at an amplitude sufficientto cause said maximum peak-to-peak excursion strokes.
 112. The apparatusas recited in claim 103, wherein the enclosed volume of said cabinet isless than 1.0 ft.³.
 113. The apparatus as recited in claim 103, whereinsaid power amplifier is mounted in said cabinet.
 114. The apparatus asrecited in claim 103, wherein said surround is formed of a material, andhas a thickness, that enables operation of said subwoofer apparatus witha maximum internal cabinet pressure substantially in excess of 0.2lbs/in².
 115. A subwoofer apparatus for use in the home, said apparatusbeing capable of producing high acoustic displacement while having arelatively small cabinet volume, said apparatus comprising: a) a cabinethaving at least one opening; b) a magnet disposed in said cabinet, saidmagnet producing a magnetic field having a flux density; c) a voice coilassembly adapted to reciprocate in said magnetic field, said voice coilassembly including a voice coil; d) a speaker diaphragm having aneffective area, driven from said voice coil assembly and mounted in saidopening to reciprocate through peak-to-peak excursion strokes; e) apower amplifier operatively connected to said voice coil and providingto said voice coil an electric current representative of an audiosignal; f) said apparatus being structured and configured so that thecombination of the maximum peak-to-peak excursion strokes, the effectivearea of the speaker diaphragm, the flux density of the magnetic field,relative to the cabinet air volume, the voice coil length, and peakcurrent therein, is such so that the maximum cabinet pressure is greaterthan 0.2 lbs./in²; and g) said apparatus being structured and configuredso that said maximum peak-to-peak excursion strokes, said voice coillength, and said flux density establish a voice coil back-emf that issubstantially greater than 13 volts rms when a 25 Hz signal is appliedto said voice coil member at an amplitude sufficient to cause saidmaximum peak-to-peak excursion strokes.
 116. The apparatus as recited inclaim 115, wherein said power amplifier operates without a powertransformer.
 117. The apparatus as recited in claim 115, wherein saidapparatus comprises a surround connected to said diaphragm and havingthickness greater than 0.02 inches.
 118. The apparatus as recited inclaim 115, wherein said apparatus comprises a surround connected to saiddiaphragm and having thickness substantially greater than 0.02 inches.119. The apparatus as recited in claim 115, wherein said maximumpeak-to-peak excursion strokes are substantially greater than 0.6inches.
 120. The apparatus as recited in claim 115, wherein saidapparatus is structured and configured so that as said speaker diaphragmand voice coil member reciprocate through said maximum peak-to-peakexcursion strokes, the maximum pressure in said cabinet is substantiallygreater than 0.2 lbs/in².
 121. The apparatus as recited in claim 115,wherein the volume enclosed by said cabinet is less than 1.0 ft.³. 122.The apparatus as recited in claim 115, wherein said power amplifier ismounted in said cabinet.
 123. The apparatus as recited in claim 115,wherein, with said peak-to-peak excursion strokes of 0.6 inches, saidflux density, said voice coil length, and said peak-to-peak excursionstrokes establish a back-emf at least as great as 13 volts rms when a 25Hz signal is supplied to said voice coil member.
 124. The apparatus asrecited in claim 115, wherein said apparatus comprises a surround formedof a material, and has a thickness, that enables operation of saidsubwoofer apparatus with a maximum cabinet pressure in excess of 0.2lbs/in².
 125. The apparatus as recited in claim 115, wherein saidapparatus comprises a surround formed of a material, and has athickness, that enables operation of said subwoofer apparatus with amaximum internal cabinet pressure substantially in excess of 0.2lbs/in².
 126. A subwoofer apparatus for use in the home, said apparatusbeing capable of producing high acoustic displacement while having arelatively small cabinet volume, said apparatus comprising: a) a cabinethaving at least one opening; b) a magnet disposed in said cabinet, saidmagnet producing a magnetic field having a flux density; c) a voice coilassembly adapted to reciprocate in said magnetic field, said voice coilassembly including a voice coil; d) a speaker diaphragm having aneffective area, driven from said voice coil assembly and mounted in saidopening to reciprocate through peak-to-peak excursion strokes; e) apower amplifier operatively connected to said voice coil and providingto said voice coil an electric current representative of an audiosignal; f) said apparatus being structured and configured so that thecombination of the maximum peak-to-peak excursion strokes, the effectivearea of the speaker diaphragm, the flux density of the magnetic field,relative to the cabinet air volume, the voice coil length, and peakcurrent therein, is such so that the maximum cabinet pressure issubstantially greater than 0.2 lbs./in²; and g) said apparatus beingstructured and configured so that said maximum peak-to-peak excursionstrokes, said voice coil length, and said flux density establish a voicecoil back-emf that is substantially greater than 13 volts rms when a 25Hz signal is applied to said voice coil member at an amplitudesufficient to cause said maximum peak-to-peak excursion strokes. 127.The apparatus as recited in claim 126, wherein said power amplifieroperates without a power transformer.
 128. The apparatus as recited inclaim 126, wherein said maximum peak-to-peak excursion strokes aregreater than 0.6 inches.
 129. The apparatus as recited in claim 126,wherein said maximum peak-to-peak excursion strokes are substantiallygreater than 0.6 inches.
 130. The apparatus as recited in claim 126,wherein said apparatus comprises a surround connected to said diaphragmand having thickness greater than 0.02 inches.
 131. The apparatus asrecited in claim 126, wherein said apparatus comprises a surroundconnected to said diaphragm and having thickness substantially greaterthan 0.02 inches.
 132. The apparatus as recited in claim 126, whereinthe volume enclosed by said cabinet is less than 1.0 ft.³.
 133. Theapparatus as recited in claim 126, wherein said power amplifier ismounted in said cabinet.
 134. The apparatus as recited in claim 126,wherein, with said peak-to-peak excursion strokes of 0.6 inches, saidflux density, said voice coil length, and said peak-to-peak excursionstrokes establish a back-emf at least as great as 13 volts rms when a 25Hz signal is supplied to said voice coil member.
 135. The apparatus asrecited in claim 126, wherein said apparatus comprises a surround formedof a material, and has a thickness, that enables operation of saidsubwoofer apparatus with a maximum internal cabinet pressuresubstantially in excess of 0.2 lbs/in².
 136. A woofer apparatus forprocessing an audio signal, said apparatus being capable of producing ahigh acoustic displacement while having a relatively small cabinetvolume, said apparatus comprising: a) a cabinet having a chamber of airvolume; b) an active driver comprising: i. a magnet disposed in saidcabinet producing a magnetic field having a flux density; ii. a voicecoil assembly positioned to reciprocate in said magnetic field throughpeak-to-peak excursion strokes, and having a voice coil adapted to beoperatively connected to a power amplifier; iii. an active speakerdiaphragm having an effective area and connected to said voice coilassembly for reciprocating motion therewith through said peak-to-peakexcursion strokes to provide an active acoustic displacement component;c) a passive radiator section comprising a passive diaphragm having aneffective area to travel through excursion strokes to provide a passiveacoustic displacement component; d) said apparatus having a maximumtotal displacement operating mode where the total of the active and thepassive displacement components is at a maximum; e) said apparatus beingstructured and configured so that as said active speaker diaphragm andsaid passive diaphragm reciprocate through their excursion strokesduring the maximum total displacement operating mode, the combination ofthe effective areas of the active speaker diaphragm and the passivediaphragm, the length of the excursion stroke of the voice coil assemblyduring the maximum total displacement operating mode, and the fluxdensity of the magnetic field is such, relative to the cabinet airvolume, the voice coil length, and peak current therein, so that themaximum cabinet pressure is greater than 0.2 lbs./in².
 137. Theapparatus as recited in claim 136, wherein maximum peak-to-peakexcursion strokes of said active speaker diaphragm are greater than 0.6inches.
 138. The apparatus as recited in claim 136, wherein said maximumpeak-to-peak excursion strokes of said active speaker diaphragm aresubstantially greater than 0.6 inches.
 139. The apparatus as recited inclaim 136, wherein there is a voice coil back-emf greater than 13 voltsrms when a 25 Hz signal is supplied to said voice coil assembly at anamplitude sufficient to cause said maximum peak-to-peak excursionstrokes of said active speaker diaphragm.
 140. The apparatus as recitedin claim 136, wherein said voice coil back-emf is substantially greaterthan 13 volts rms when a 25 Hz signal is supplied to said voice coilassembly at an amplitude sufficient to cause said maximum peak-to-peakexcursion strokes of said active speaker diaphragm.
 141. The apparatusas recited in claim 136, wherein, with said peak-to-peak excursionstrokes of said active speaker diaphragm of 0.6 inches, said fluxdensity, said voice coil length, and said peak-to-peak excursion strokesestablish a back-emf at least as great as 13 volts rms when a 25 Hzsignal is supplied to said voice coil assembly.
 142. The apparatus asrecited in claim 136, wherein there is a surround connecting to saidactive speaker diaphragm, and said surround has a thickness greater than0.02 inches.
 143. The apparatus as recited in claim 142, wherein saidsurround has a thickness substantially greater than 0.02 inches. 144.The apparatus as recited in claim 136, wherein the air volume of saidcabinet is less than 1.0 ft.³.
 145. The apparatus as recited in claim136, wherein said apparatus further comprises a power amplifier which ismounted in said cabinet and connected to said voice coil assembly tosupply a signal representative of an audio signal to drive said voicecoil assembly.
 146. The apparatus as recited in claim 142, wherein saidpower amplifier operates without a power transformer.
 147. The apparatusas recited in claim 136, wherein said apparatus comprises a surroundformed of a material, and has a thickness, that enables operation ofsaid subwoofer apparatus with a maximum internal cabinet pressure inexcess of 0.2 lbs/in².
 148. The apparatus as recited in claim 136,wherein said apparatus comprises a surround formed of a material, andhas a thickness, that enables operation of said subwoofer apparatus witha maximum internal cabinet pressure substantially in excess of 0.2lbs/in².
 149. The apparatus as recited in claim 136, wherein saidapparatus further comprises a surround having an edgeroll that has anoutside diameter dimension greater than 1.0 inches.